Background： Estimation of tree diversity at broader scale is important for conservation planning. Tree diversity should be measured and understood in terms of diversity and evenness, two integral components to descri...Background： Estimation of tree diversity at broader scale is important for conservation planning. Tree diversity should be measured and understood in terms of diversity and evenness, two integral components to describe the structure of a biological community. Variation of the tree diversity and evenness with elevation, topographic relief, aspect, terrain shape, slope, soil nutrient, solar radiation etc. are well documented. Methods： Present study explores the variation of tree diversity （measured as Shannon diversity and evenness indices） of Majella National Park, italy with five available forest types namely evergreen oak woods, deciduous oak woods, blacWaleppo pine stands, hop-hornbeam forest and beech forest, using satellite, environmental and field data. Results： Hop-hornbeam forest was found to be most diverse and even while evergreen Oak woods was the lowest diverse and even. Diversity and evenness of forest types were concurrent to each other i.e. forest type which was more diverse was also more even. As a broad pattern, majority portion of the study area belonged to medium diversity and high evenness class. Conclusions： Satellite images and other GIS data proved useful tools in monitoring variation of tree diversity and evenness across various forest types. Present study findings may have implications in prioritizing conservation zones of high tree diversity at Majella.展开更多
Hepatocellular carcinoma(HCC) is one of the deadliest cancers in the world and is associated with a high risk of recurrence. The development of a wide range of new therapies is therefore essential. In this study, from...Hepatocellular carcinoma(HCC) is one of the deadliest cancers in the world and is associated with a high risk of recurrence. The development of a wide range of new therapies is therefore essential. In this study, from the perspective of supportive therapy for the prevention of HCC recurrence and preservation of liver function in HCC patients, we surveyed a variety of different therapeutic agents. We show that branched chain amino acids(BCAA) supplementation and late evening snack with BCAA, strategies that address issues of protein-energy malnutrition, are important for liver cirrhotic patients with HCC. For chemoprevention of HCC recurrence, we show that viral control after radical treatment is important. We also reviewed the therapeutic potential of antiviral drugs, sorafenib, peretinoin, iron chelators. Sorafenib is a kinase inhibitor and a standard therapy in the treatment of advanced HCC. Peretinoin is a vitamin A-like molecule that targets the retinoid nuclear receptor to induce apoptosis and inhibit tumor growth in HCC cells. Iron chelators, such as deferoxamine and deferasirox, act to prevent cancer cell growth. These chelators may have potential as combination therapies in conjunction with peretinoin. Finally, we review the potential inhibitory effect of bone marrow cells on hepatocarcinogenesis.展开更多
Peripheral nerve injuries with a poor prognosis are common.Evening primrose oil（EPO） has beneficial biological effects and immunomodulatory properties.Since electrical activity plays a major role in neural regenerat...Peripheral nerve injuries with a poor prognosis are common.Evening primrose oil（EPO） has beneficial biological effects and immunomodulatory properties.Since electrical activity plays a major role in neural regeneration,the present study investigated the effects of electrical stimulation（ES）,combined with evening primrose oil（EPO）,on sciatic nerve function after a crush injury in rats.In anesthetized rats,the sciatic nerve was crushed using small haemostatic forceps followed by ES and/or EPO treatment for 4 weeks.Functional recovery of the sciatic nerve was assessed using the sciatic functional index.Histopathological changes of gastrocnemius muscle atrophy were investigated by light microscopy.Electrophysiological changes were assessed by the nerve conduction velocity of sciatic nerves.Immunohistochemistry was used to determine the remyelination of the sciatic nerve following the interventions.EPO ＋ ES,EPO,and ES obviously improved sciatic nerve function assessed by the sciatic functional index and nerve conduction velocity of the sciatic nerve at 28 days after operation.Expression of the peripheral nerve remyelination marker,protein zero（P0）,was increased in the treatment groups at 28 days after operation.Muscle atrophy severity was decreased significantly while the nerve conduction velocity was increased significantly in rats with sciatic nerve injury in the injury ＋ EPO ＋ ES group than in the EPO or ES group.Totally speaking,the combined use of EPO and ES may produce an improving effect on the function of sciatic nerves injured by a crush.The increased expression of P0 may have contributed to improving the functional effects of combination therapy with EPO and ES as well as the electrophysiological and histopathological features of the injured peripheral nerve.展开更多
As Lewis proposed his octet rule, itself inspired by Abegg’s rule, that a molecule is stable when all its composing atoms have eight electrons in their valence shell, it perfectly applied to the vast majority of know...As Lewis proposed his octet rule, itself inspired by Abegg’s rule, that a molecule is stable when all its composing atoms have eight electrons in their valence shell, it perfectly applied to the vast majority of known stable molecules. Only a few stable molecules were known that didn’t fall under this rule, such as PCl5 and SF6, and Lewis chose to leave them aside at the time of his research. With further advances in chemistry, more exceptions to this rule of eight have been found, usually with the central atom of the structure having more or less than eight electrons in its valence shell. Theories have been developed in order to modify the octet rule to suit these molecules, defining these as hyper- or hypo-valent molecules and using other configurations for the electrons. The present paper aims to propose a representation rule for gaseous single-bonded molecules that makes it possible to reconcile both;molecules following the octet theory and those which do not. In this representation rule, each element of the molecule is subscripted with two numbers that follow a set of simple criteria. The first represents the number of valence electrons of the element;while the second is calculated by adding the first number to the number of the element’s covalent bonds within the molecule. The latter is equal to eight for organic molecules following the octet rule. Molecules being exceptions to the octet rule are now encompassed by this new even-odd rule: they have a valid chemical structural formula in which the second number is even but not always equal to eight. Both rules—octet and even-odd—are discussed and compared, using several well-known gaseous molecules having one or several single-bonded elements. A future paper will discuss the application of the even-odd rule to charged molecules.展开更多
Lewis developed a 2D-representation of molecules, charged or uncharged, known as structural formula, and stated the criteria to draw it. At the time, the vast majority of known molecules followed the octet-rule, one o...Lewis developed a 2D-representation of molecules, charged or uncharged, known as structural formula, and stated the criteria to draw it. At the time, the vast majority of known molecules followed the octet-rule, one of Lewis’s criteria. The same method was however rapidly applied to represent compounds that do not follow the octet-rule, i.e. compounds for which some of the composing atoms have greater or less than eight electrons in their valence shell. In a previous paper, an even-odd rule was proposed and shown to apply to both types of uncharged molecules. In the present paper, the even-odd rule is extended with the objective to encompass all single-bonded ions in one group: Lewis’s ions, hypo- and hypervalent ions. The base of the even-odd representation is compatible with Lewis’s diagram. Additionally, each atom is subscripted with an even number calculated by adding the valence number, the number of covalent bonds of the element, and its electrical charge. This paper describes how to calculate the latter number and in doing so, how charge and electron-pairs can actually be precisely localized. Using ions known to be compatible with Lewis’s rule of eight, the even-odd rule is compared with the former. The even-odd rule is then applied to ions known as hypo- or hypervalent. An interesting side effect of the presented rule is that charge and electron-pairs are unambiguously assigned to one of the atoms composing the single-charged ion. Ions that follow the octet rule and ions that do not, are thus reconciled in one group called “electron-paired ions” due to the absence of unpaired electrons. A future paper will focus on the connection between the even-odd rule and molecules or ions having multiple bonds.展开更多
In organic chemistry, as defined by Abegg, Kossel, Lewis and Langmuir, compounds are normally represented using structural formulas called Lewis structures. In these structures, the octet rule is used to define the nu...In organic chemistry, as defined by Abegg, Kossel, Lewis and Langmuir, compounds are normally represented using structural formulas called Lewis structures. In these structures, the octet rule is used to define the number of covalent bonds that each atom forms with its neighbors and multiple bonds are frequent. Lewis’ octet rule has unfortunately shown limitations very early when applied to non-organic compounds: most of them remain incompatible with the “rule of eight” and location of charges is uncertain. In an attempt to unify structural formulas of octet and non-octet molecules or single-charge ions, an even-odd rule was recently proposed, together with a procedure to locate charge precisely. This even-odd rule has introduced a charge-dependent effective-valence number calculated for each atom. With this number and the number of covalent bonds of each element, two even numbers are calculated. These numbers are both used to understand and draw structuralformulas of single-covalent-bonded compounds. In the present paper, a procedure is proposed to adjust structural formulas of compounds that are commonly represented with multiple bonds. In order to keep them compatible with the even-odd rule, they will be represented using only single covalent bonds. The procedure will then describe the consequences of bond simplification on charges locations. The newly obtained representations are compared to their conventional structural formulas, i.e. single-bond representation vs. multiple-bond structures. Throughout the comparison process, charges are precisely located and assigned to specific atoms. After discussion of particular cases of compounds, the paper finally concludes that a rule limiting representations of multiplecovalent bonds to single covalent bonds, seems to be suitable for numerous known compounds.展开更多
Two-colour stepwise excitation and photoionization schemes are adopted to study the spectra of high-lying states of the Sm atom. These bound even-parity states are excited with three different excitation paths from th...Two-colour stepwise excitation and photoionization schemes are adopted to study the spectra of high-lying states of the Sm atom. These bound even-parity states are excited with three different excitation paths from the 4f66s6p7DJ （J = 1, 2, 3） intermediate states, respectively. They are probed by photoionization process with an extra photon driving them to the continuum states. In this experiment, 270 states are detected in an energy range from 36160 cm-1 to 42250 cm-1, 109 of which are newly discovered, while the rest of them are confirmed to be the energy levels reported previously. Furthermore, based on the J-momentum selection rules of three excitation paths, a unique assignment of J-momentum for all observed states is determined, eliminating all remaining ambiguities in the literature. Finally, 53 single-colour transitions originating from the scanning laser are also identified. For all the relevant transitions, the information about their relative intensities is also given in the paper.展开更多
In the course of time, numerous rules were proposed to predict how atoms connect through covalent bonds. Based on the classification of elements in the periodic table, the rule of eight was first proposed to draw form...In the course of time, numerous rules were proposed to predict how atoms connect through covalent bonds. Based on the classification of elements in the periodic table, the rule of eight was first proposed to draw formulas of organic compounds. The later named octet rule exhibited shortcomings when applied to inorganic compounds. Another rule, the rule of two, using covalent bonds between atoms, was proposed as an attempt to unify description of organic and inorganic molecules. This rule unfortunately never managed to expand the field of application of the octet rule to inorganic compounds. In order to conciliate organic and inorganic compounds, the recently put forward even-odd and the isoelectronicity rules suggest the creation of one group of compounds with pairs of electrons. These rules compass the rule of two for covalent bonds as well as the octet rule for organic compounds and suggest transforming bonds of multi-bonded compounds in order to unify representations of both groups of compounds. The aim of the present paper is fourfold: to extend the rule of two to every atom shells;to replace the well-known octet rule by the even-odd rule;to apply the isoelectronicity rule to each atom and to reduce the influence range of the charge of an atom in a compound. According to both rules, the drawing of one atom with its single-covalent bonds is described with electron pairs and charge positions. To illustrate the rules, they are applied to 3D configurations of clusters.展开更多
Ions or molecules are said to be isoelectronic if they are composed of different elements but have the same number of electrons, the same number of covalent bonds and the same structure. This criterion is unfortunatel...Ions or molecules are said to be isoelectronic if they are composed of different elements but have the same number of electrons, the same number of covalent bonds and the same structure. This criterion is unfortunately not sufficient to ensure that a chemical structure is a valid chemical compound. In a previous article, a procedure has been described to draw 2D valid structural formulas: the even-odd rule. This rule has been applied first to single-bonded molecules then to single-charged single-bonded ions. It covers hypovalent, hypervalent or classic Lewis’ octet compounds. The funding principle of the even-odd rule is that each atom of the compound possesses an outer-shell filled only with pairs of electrons. The application of this rule guarantees validity of any single-covalent-bond chemical structure. In the present paper, this even-odd rule and its electron-pair criterion are checked for coherence with an effective-valence isoelectronic rule using numerous known compounds having single-covalent-bond connections. The test addresses Lewis’ octet ions or molecules as well as hypovalent and hypervalent compounds. The article concludes that the even-odd rule and the effective-valence isoelectronicity rule are coherent for known single-covalent-bond chemical compounds.展开更多
A crystal is a highly organized arrangement of atoms in a solid, wherein a unit cell is periodically repeated to form the crystal pattern. A unit cell is composed of atoms that are connected to some of their first nei...A crystal is a highly organized arrangement of atoms in a solid, wherein a unit cell is periodically repeated to form the crystal pattern. A unit cell is composed of atoms that are connected to some of their first neighbors by chemical bonds. A recent rule, entitled the even-odd rule, introduced a new way to calculate the number of covalent bonds around an atom. It states that around an uncharged atom, the number of bonds and the number of electrons have the same parity. In the case of a charged atom on the contrary, both numbers have different parity. The aim of the present paper is to challenge the even-odd rule on chemical bonds in well-known crystal structures. According to the rule, atoms are supposed to be bonded exclusively through single-covalent bonds. A distinctive criterion, only applicable to crystals, states that atoms cannot build more than 8 chemical bonds, as opposed to the classical model, where each atom in a crystal is connected to every first neighbor without limitation. Electrical charges can be assigned to specific atoms in order to compensate for extra or missing bonds. More specifically the article considers di-atomic body-centered-cubic, tetra-atomic and dodeca-atomic single-face-centered-cubic crystals. In body-centered crystals, atoms are interconnected by 8 covalent bonds. In face-centered crystal, the unit cell contains 4 or 12 atoms. For di-element crystals, the total number of bonds for both elements is found to be identical. The neutrality of the unit cell is obtained with an opposite charge on the nearest or second-nearest neighbor. To conclude, the even-odd rule is applicable to a wide number of compounds in known cubic structures and the number of chemical bonds per atom is not related to the valence of the elements in the periodic table.展开更多
The recently introduced even-odd rule has been shown to successfully represent chemical structures of ions and molecules. While comparing available drawings in the scientific literature with the list of compounds pred...The recently introduced even-odd rule has been shown to successfully represent chemical structures of ions and molecules. While comparing available drawings in the scientific literature with the list of compounds predicted by the even-odd rule, it became however obvious that existing compounds are fewer than expected. Several predicted compounds involving many covalent bonds have apparently never been experimentally observed. Neutral oxygen for instance is expected to have 6 valence electrons, whereas oxygen can only build a maximum of two bonds, as in water. This specificity is observed for elements in the top-right corner of the periodic table. For compounds to contain only single covalent bonds, and thus follow the even-odd rule, further explanations are necessary. The present paper proposes that those specific elements experience a transfer of electrons from the valence shell into the inner shell, making them unavailable for further bonding. These elements will be described as organic, hereby providing a clear and hopefully unifying definition of the term. In opposition, inorganic elements have a constant inner shell no matter their electrical state or the number of bonds they maintain. More than 70 compounds involving 11 elements of the main group are studied, revealing a progression from fully inorganic elements at the left of the periodic table to fully organic elements. The transition between inorganic or organic elements is made of few elements that take an organic form when negatively charged;they are labelled semi-organic. The article concludes that the fully organic elements of the main group are Oxygen and Fluorine, whereas semi-organic elements are more numerous: C, N, S, Cl, Se, Br and I. Thus, the even-odd rule becomes fully compatible with scientific knowledge of compounds in liquid or gaseous phase.展开更多
A decrease in temperature will eventually turn a gas into liquid and then into a solid. Each of these phase change shows a higher degree in cohesion of molecules. While it is usually admitted that molecules in solids ...A decrease in temperature will eventually turn a gas into liquid and then into a solid. Each of these phase change shows a higher degree in cohesion of molecules. While it is usually admitted that molecules in solids form additional connections, the cohesion of molecules in liquids is usually explained by changes in kinetics of molecules. Given that the density of a solid is nearly the same than that of a liquid, the present paper assumes a different stand and considers that connections between molecules must be similar in liquids and in solids. The difference between gas, in which molecules are entirely loose, and liquid, is therefore the presence of an additional connection between gaseous molecules. This paper describes how and where these connections are built with the help of a few rules and a “specific periodic table for liquids”. The coherence of this approach is reinforced by its capacity to explain phase change of forty well-known molecules containing inorganic and organic elements.展开更多
Following the introduction of the new even-odd and isoelectronic rules and definitions affecting the understanding of electronic structure and bonds, the author has thought necessary to summarize understandings in the...Following the introduction of the new even-odd and isoelectronic rules and definitions affecting the understanding of electronic structure and bonds, the author has thought necessary to summarize understandings in the form of a table. The classical periodic table, a simple tool used by generations of physicists, is here extended to become a useful tool aimed specifically at chemists. In chemistry, position and number of covalent bonds of each atom are needed, as well as the exact location of charges. The table gives the number of possible bonds for each element and reveals how it is affected by charges. Additionally, the specific table indicates for each atom its isoelectronic elements and highlights the distinction between organic and inorganic elements. Discussion is led on the first two rows of the table by successfully comparing its statement with more than 50 well-known liquid and gaseous compounds.展开更多
This paper has investigated quantum teleportation of even and odd coherent states in terms of the EPR entanglement states for continuous variables. It discusses the relationship between the fidelity and the entangleme...This paper has investigated quantum teleportation of even and odd coherent states in terms of the EPR entanglement states for continuous variables. It discusses the relationship between the fidelity and the entanglement of EPR states, which is characterized by the degree of squeezing and the gain of classical channels. It shows that the quality of teleporting quantum states also depends on the characteristics of the states themselves. The properties of teleporting even and odd coherent states at different intensities are investigated. The difference of teleporting two such kinds of quantum states are analysed based on the quantum distance function.展开更多
The method of Zeng et al. (1991) employed diameter growth to estimate the transition probability of the matrix model in uneven-aged forest stands. In this paper the Weibull distribution for even-aged forest stands ins...The method of Zeng et al. (1991) employed diameter growth to estimate the transition probability of the matrix model in uneven-aged forest stands. In this paper the Weibull distribution for even-aged forest stands instead of uniform distribution chosen by Zeng is used. By comparing the results of the improved method with those of the original method of Zeng, it turns out that the improved method of Zeng given in this paper is more efficient.展开更多
We calculated the harmonic spectra generated from the asymmetric molecules of HD^＋ and HeH^2＋. It is found that HD＋produces only odd harmonics, while HeH^2＋produces both odd and even harmonics. Further analysis re...We calculated the harmonic spectra generated from the asymmetric molecules of HD^＋ and HeH^2＋. It is found that HD＋produces only odd harmonics, while HeH^2＋produces both odd and even harmonics. Further analysis reveals that for both HD^＋ and HeH^2＋, the nuclear dipole acceleration can generate even harmonics, but it is three orders of magnitude lower than that of the electron. Hence, the electronic dipole acceleration dominates the harmonic generation. For HD^＋,the electronic dipole acceleration only contributes to the generation of odd harmonics, but for HeH^2＋it contributes to the generation of both odd and even harmonics. Besides, one concept of the broken degree of system-symmetry is proposed to explain the different odd-even property between the harmonic spectra of HD^＋ and HeH^2＋.展开更多
A series of bowlic cyclotriveratrylenes（CTV） with peripheral groups with different lengths were synthesized.These compounds were investigated by diferential scanning calorimetry and hot stage coupled polarizing micr...A series of bowlic cyclotriveratrylenes（CTV） with peripheral groups with different lengths were synthesized.These compounds were investigated by diferential scanning calorimetry and hot stage coupled polarizing microscopy.Several CTV derivatives show thermotropic liquid crystalline properties.The experimental results of their thermotropic liquid crystalline behavior indicate that the clear points,the entropy changes of melting points,the crystallization temperatures,and their entropy changes all exhibited an evident odd-even effect except the melting points,which decreased monotonously with the increase of the length of the alkoxy groups.The parameter values of CTVs with even number carbon atoms were larger than those of CTVs with odd number.When the length of alkoxyl chains was even longer,a monotonous decrease occured.Nevertheless,in the case of the entropy changes of both melting points and crystallization temperatures,the effect was valid for all the six species,and therefore,the whole curves presented as a zig-zag form.展开更多
文摘Background： Estimation of tree diversity at broader scale is important for conservation planning. Tree diversity should be measured and understood in terms of diversity and evenness, two integral components to describe the structure of a biological community. Variation of the tree diversity and evenness with elevation, topographic relief, aspect, terrain shape, slope, soil nutrient, solar radiation etc. are well documented. Methods： Present study explores the variation of tree diversity （measured as Shannon diversity and evenness indices） of Majella National Park, italy with five available forest types namely evergreen oak woods, deciduous oak woods, blacWaleppo pine stands, hop-hornbeam forest and beech forest, using satellite, environmental and field data. Results： Hop-hornbeam forest was found to be most diverse and even while evergreen Oak woods was the lowest diverse and even. Diversity and evenness of forest types were concurrent to each other i.e. forest type which was more diverse was also more even. As a broad pattern, majority portion of the study area belonged to medium diversity and high evenness class. Conclusions： Satellite images and other GIS data proved useful tools in monitoring variation of tree diversity and evenness across various forest types. Present study findings may have implications in prioritizing conservation zones of high tree diversity at Majella.
基金Supported by Japan Society for the Promotion of Science,KIBAN-C,No.26461009
文摘Hepatocellular carcinoma(HCC) is one of the deadliest cancers in the world and is associated with a high risk of recurrence. The development of a wide range of new therapies is therefore essential. In this study, from the perspective of supportive therapy for the prevention of HCC recurrence and preservation of liver function in HCC patients, we surveyed a variety of different therapeutic agents. We show that branched chain amino acids(BCAA) supplementation and late evening snack with BCAA, strategies that address issues of protein-energy malnutrition, are important for liver cirrhotic patients with HCC. For chemoprevention of HCC recurrence, we show that viral control after radical treatment is important. We also reviewed the therapeutic potential of antiviral drugs, sorafenib, peretinoin, iron chelators. Sorafenib is a kinase inhibitor and a standard therapy in the treatment of advanced HCC. Peretinoin is a vitamin A-like molecule that targets the retinoid nuclear receptor to induce apoptosis and inhibit tumor growth in HCC cells. Iron chelators, such as deferoxamine and deferasirox, act to prevent cancer cell growth. These chelators may have potential as combination therapies in conjunction with peretinoin. Finally, we review the potential inhibitory effect of bone marrow cells on hepatocarcinogenesis.
基金financially supported by the Neuroscience Research Center of the Tabriz University of Medical Sciences,Tabriz,Iran
文摘Peripheral nerve injuries with a poor prognosis are common.Evening primrose oil（EPO） has beneficial biological effects and immunomodulatory properties.Since electrical activity plays a major role in neural regeneration,the present study investigated the effects of electrical stimulation（ES）,combined with evening primrose oil（EPO）,on sciatic nerve function after a crush injury in rats.In anesthetized rats,the sciatic nerve was crushed using small haemostatic forceps followed by ES and/or EPO treatment for 4 weeks.Functional recovery of the sciatic nerve was assessed using the sciatic functional index.Histopathological changes of gastrocnemius muscle atrophy were investigated by light microscopy.Electrophysiological changes were assessed by the nerve conduction velocity of sciatic nerves.Immunohistochemistry was used to determine the remyelination of the sciatic nerve following the interventions.EPO ＋ ES,EPO,and ES obviously improved sciatic nerve function assessed by the sciatic functional index and nerve conduction velocity of the sciatic nerve at 28 days after operation.Expression of the peripheral nerve remyelination marker,protein zero（P0）,was increased in the treatment groups at 28 days after operation.Muscle atrophy severity was decreased significantly while the nerve conduction velocity was increased significantly in rats with sciatic nerve injury in the injury ＋ EPO ＋ ES group than in the EPO or ES group.Totally speaking,the combined use of EPO and ES may produce an improving effect on the function of sciatic nerves injured by a crush.The increased expression of P0 may have contributed to improving the functional effects of combination therapy with EPO and ES as well as the electrophysiological and histopathological features of the injured peripheral nerve.
文摘As Lewis proposed his octet rule, itself inspired by Abegg’s rule, that a molecule is stable when all its composing atoms have eight electrons in their valence shell, it perfectly applied to the vast majority of known stable molecules. Only a few stable molecules were known that didn’t fall under this rule, such as PCl5 and SF6, and Lewis chose to leave them aside at the time of his research. With further advances in chemistry, more exceptions to this rule of eight have been found, usually with the central atom of the structure having more or less than eight electrons in its valence shell. Theories have been developed in order to modify the octet rule to suit these molecules, defining these as hyper- or hypo-valent molecules and using other configurations for the electrons. The present paper aims to propose a representation rule for gaseous single-bonded molecules that makes it possible to reconcile both;molecules following the octet theory and those which do not. In this representation rule, each element of the molecule is subscripted with two numbers that follow a set of simple criteria. The first represents the number of valence electrons of the element;while the second is calculated by adding the first number to the number of the element’s covalent bonds within the molecule. The latter is equal to eight for organic molecules following the octet rule. Molecules being exceptions to the octet rule are now encompassed by this new even-odd rule: they have a valid chemical structural formula in which the second number is even but not always equal to eight. Both rules—octet and even-odd—are discussed and compared, using several well-known gaseous molecules having one or several single-bonded elements. A future paper will discuss the application of the even-odd rule to charged molecules.
文摘Lewis developed a 2D-representation of molecules, charged or uncharged, known as structural formula, and stated the criteria to draw it. At the time, the vast majority of known molecules followed the octet-rule, one of Lewis’s criteria. The same method was however rapidly applied to represent compounds that do not follow the octet-rule, i.e. compounds for which some of the composing atoms have greater or less than eight electrons in their valence shell. In a previous paper, an even-odd rule was proposed and shown to apply to both types of uncharged molecules. In the present paper, the even-odd rule is extended with the objective to encompass all single-bonded ions in one group: Lewis’s ions, hypo- and hypervalent ions. The base of the even-odd representation is compatible with Lewis’s diagram. Additionally, each atom is subscripted with an even number calculated by adding the valence number, the number of covalent bonds of the element, and its electrical charge. This paper describes how to calculate the latter number and in doing so, how charge and electron-pairs can actually be precisely localized. Using ions known to be compatible with Lewis’s rule of eight, the even-odd rule is compared with the former. The even-odd rule is then applied to ions known as hypo- or hypervalent. An interesting side effect of the presented rule is that charge and electron-pairs are unambiguously assigned to one of the atoms composing the single-charged ion. Ions that follow the octet rule and ions that do not, are thus reconciled in one group called “electron-paired ions” due to the absence of unpaired electrons. A future paper will focus on the connection between the even-odd rule and molecules or ions having multiple bonds.
文摘In organic chemistry, as defined by Abegg, Kossel, Lewis and Langmuir, compounds are normally represented using structural formulas called Lewis structures. In these structures, the octet rule is used to define the number of covalent bonds that each atom forms with its neighbors and multiple bonds are frequent. Lewis’ octet rule has unfortunately shown limitations very early when applied to non-organic compounds: most of them remain incompatible with the “rule of eight” and location of charges is uncertain. In an attempt to unify structural formulas of octet and non-octet molecules or single-charge ions, an even-odd rule was recently proposed, together with a procedure to locate charge precisely. This even-odd rule has introduced a charge-dependent effective-valence number calculated for each atom. With this number and the number of covalent bonds of each element, two even numbers are calculated. These numbers are both used to understand and draw structuralformulas of single-covalent-bonded compounds. In the present paper, a procedure is proposed to adjust structural formulas of compounds that are commonly represented with multiple bonds. In order to keep them compatible with the even-odd rule, they will be represented using only single covalent bonds. The procedure will then describe the consequences of bond simplification on charges locations. The newly obtained representations are compared to their conventional structural formulas, i.e. single-bond representation vs. multiple-bond structures. Throughout the comparison process, charges are precisely located and assigned to specific atoms. After discussion of particular cases of compounds, the paper finally concludes that a rule limiting representations of multiplecovalent bonds to single covalent bonds, seems to be suitable for numerous known compounds.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10574098 and 10674102)the Natural Science Foundation of Tianjin, China (Grant No. 05YFJMJC05200)
文摘Two-colour stepwise excitation and photoionization schemes are adopted to study the spectra of high-lying states of the Sm atom. These bound even-parity states are excited with three different excitation paths from the 4f66s6p7DJ （J = 1, 2, 3） intermediate states, respectively. They are probed by photoionization process with an extra photon driving them to the continuum states. In this experiment, 270 states are detected in an energy range from 36160 cm-1 to 42250 cm-1, 109 of which are newly discovered, while the rest of them are confirmed to be the energy levels reported previously. Furthermore, based on the J-momentum selection rules of three excitation paths, a unique assignment of J-momentum for all observed states is determined, eliminating all remaining ambiguities in the literature. Finally, 53 single-colour transitions originating from the scanning laser are also identified. For all the relevant transitions, the information about their relative intensities is also given in the paper.
文摘In the course of time, numerous rules were proposed to predict how atoms connect through covalent bonds. Based on the classification of elements in the periodic table, the rule of eight was first proposed to draw formulas of organic compounds. The later named octet rule exhibited shortcomings when applied to inorganic compounds. Another rule, the rule of two, using covalent bonds between atoms, was proposed as an attempt to unify description of organic and inorganic molecules. This rule unfortunately never managed to expand the field of application of the octet rule to inorganic compounds. In order to conciliate organic and inorganic compounds, the recently put forward even-odd and the isoelectronicity rules suggest the creation of one group of compounds with pairs of electrons. These rules compass the rule of two for covalent bonds as well as the octet rule for organic compounds and suggest transforming bonds of multi-bonded compounds in order to unify representations of both groups of compounds. The aim of the present paper is fourfold: to extend the rule of two to every atom shells;to replace the well-known octet rule by the even-odd rule;to apply the isoelectronicity rule to each atom and to reduce the influence range of the charge of an atom in a compound. According to both rules, the drawing of one atom with its single-covalent bonds is described with electron pairs and charge positions. To illustrate the rules, they are applied to 3D configurations of clusters.
文摘Ions or molecules are said to be isoelectronic if they are composed of different elements but have the same number of electrons, the same number of covalent bonds and the same structure. This criterion is unfortunately not sufficient to ensure that a chemical structure is a valid chemical compound. In a previous article, a procedure has been described to draw 2D valid structural formulas: the even-odd rule. This rule has been applied first to single-bonded molecules then to single-charged single-bonded ions. It covers hypovalent, hypervalent or classic Lewis’ octet compounds. The funding principle of the even-odd rule is that each atom of the compound possesses an outer-shell filled only with pairs of electrons. The application of this rule guarantees validity of any single-covalent-bond chemical structure. In the present paper, this even-odd rule and its electron-pair criterion are checked for coherence with an effective-valence isoelectronic rule using numerous known compounds having single-covalent-bond connections. The test addresses Lewis’ octet ions or molecules as well as hypovalent and hypervalent compounds. The article concludes that the even-odd rule and the effective-valence isoelectronicity rule are coherent for known single-covalent-bond chemical compounds.
文摘A crystal is a highly organized arrangement of atoms in a solid, wherein a unit cell is periodically repeated to form the crystal pattern. A unit cell is composed of atoms that are connected to some of their first neighbors by chemical bonds. A recent rule, entitled the even-odd rule, introduced a new way to calculate the number of covalent bonds around an atom. It states that around an uncharged atom, the number of bonds and the number of electrons have the same parity. In the case of a charged atom on the contrary, both numbers have different parity. The aim of the present paper is to challenge the even-odd rule on chemical bonds in well-known crystal structures. According to the rule, atoms are supposed to be bonded exclusively through single-covalent bonds. A distinctive criterion, only applicable to crystals, states that atoms cannot build more than 8 chemical bonds, as opposed to the classical model, where each atom in a crystal is connected to every first neighbor without limitation. Electrical charges can be assigned to specific atoms in order to compensate for extra or missing bonds. More specifically the article considers di-atomic body-centered-cubic, tetra-atomic and dodeca-atomic single-face-centered-cubic crystals. In body-centered crystals, atoms are interconnected by 8 covalent bonds. In face-centered crystal, the unit cell contains 4 or 12 atoms. For di-element crystals, the total number of bonds for both elements is found to be identical. The neutrality of the unit cell is obtained with an opposite charge on the nearest or second-nearest neighbor. To conclude, the even-odd rule is applicable to a wide number of compounds in known cubic structures and the number of chemical bonds per atom is not related to the valence of the elements in the periodic table.
文摘The recently introduced even-odd rule has been shown to successfully represent chemical structures of ions and molecules. While comparing available drawings in the scientific literature with the list of compounds predicted by the even-odd rule, it became however obvious that existing compounds are fewer than expected. Several predicted compounds involving many covalent bonds have apparently never been experimentally observed. Neutral oxygen for instance is expected to have 6 valence electrons, whereas oxygen can only build a maximum of two bonds, as in water. This specificity is observed for elements in the top-right corner of the periodic table. For compounds to contain only single covalent bonds, and thus follow the even-odd rule, further explanations are necessary. The present paper proposes that those specific elements experience a transfer of electrons from the valence shell into the inner shell, making them unavailable for further bonding. These elements will be described as organic, hereby providing a clear and hopefully unifying definition of the term. In opposition, inorganic elements have a constant inner shell no matter their electrical state or the number of bonds they maintain. More than 70 compounds involving 11 elements of the main group are studied, revealing a progression from fully inorganic elements at the left of the periodic table to fully organic elements. The transition between inorganic or organic elements is made of few elements that take an organic form when negatively charged;they are labelled semi-organic. The article concludes that the fully organic elements of the main group are Oxygen and Fluorine, whereas semi-organic elements are more numerous: C, N, S, Cl, Se, Br and I. Thus, the even-odd rule becomes fully compatible with scientific knowledge of compounds in liquid or gaseous phase.
文摘A decrease in temperature will eventually turn a gas into liquid and then into a solid. Each of these phase change shows a higher degree in cohesion of molecules. While it is usually admitted that molecules in solids form additional connections, the cohesion of molecules in liquids is usually explained by changes in kinetics of molecules. Given that the density of a solid is nearly the same than that of a liquid, the present paper assumes a different stand and considers that connections between molecules must be similar in liquids and in solids. The difference between gas, in which molecules are entirely loose, and liquid, is therefore the presence of an additional connection between gaseous molecules. This paper describes how and where these connections are built with the help of a few rules and a “specific periodic table for liquids”. The coherence of this approach is reinforced by its capacity to explain phase change of forty well-known molecules containing inorganic and organic elements.
文摘Following the introduction of the new even-odd and isoelectronic rules and definitions affecting the understanding of electronic structure and bonds, the author has thought necessary to summarize understandings in the form of a table. The classical periodic table, a simple tool used by generations of physicists, is here extended to become a useful tool aimed specifically at chemists. In chemistry, position and number of covalent bonds of each atom are needed, as well as the exact location of charges. The table gives the number of possible bonds for each element and reveals how it is affected by charges. Additionally, the specific table indicates for each atom its isoelectronic elements and highlights the distinction between organic and inorganic elements. Discussion is led on the first two rows of the table by successfully comparing its statement with more than 50 well-known liquid and gaseous compounds.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10434080, 10374062, 60578018）, NSFC-RFBR Joint Program, Research Funds for Returned Scholar Abroad from Shanxi Province and also supported by the CFKSTIP （Grant No 705010） and PCSIRT from Ministry of Education of China.
文摘This paper has investigated quantum teleportation of even and odd coherent states in terms of the EPR entanglement states for continuous variables. It discusses the relationship between the fidelity and the entanglement of EPR states, which is characterized by the degree of squeezing and the gain of classical channels. It shows that the quality of teleporting quantum states also depends on the characteristics of the states themselves. The properties of teleporting even and odd coherent states at different intensities are investigated. The difference of teleporting two such kinds of quantum states are analysed based on the quantum distance function.
基金This paper was supported by the National Natural Science Foundation of China
文摘The method of Zeng et al. (1991) employed diameter growth to estimate the transition probability of the matrix model in uneven-aged forest stands. In this paper the Weibull distribution for even-aged forest stands instead of uniform distribution chosen by Zeng is used. By comparing the results of the improved method with those of the original method of Zeng, it turns out that the improved method of Zeng given in this paper is more efficient.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11404153,11135002,11475076,and 11405077)the Fundamental Research Funds for the Central Universities of China(Grants Nos.lzujbky-2016-29,lzujbky-2016-31,and lzujbky-2016-209)
文摘We calculated the harmonic spectra generated from the asymmetric molecules of HD^＋ and HeH^2＋. It is found that HD＋produces only odd harmonics, while HeH^2＋produces both odd and even harmonics. Further analysis reveals that for both HD^＋ and HeH^2＋, the nuclear dipole acceleration can generate even harmonics, but it is three orders of magnitude lower than that of the electron. Hence, the electronic dipole acceleration dominates the harmonic generation. For HD^＋,the electronic dipole acceleration only contributes to the generation of odd harmonics, but for HeH^2＋it contributes to the generation of both odd and even harmonics. Besides, one concept of the broken degree of system-symmetry is proposed to explain the different odd-even property between the harmonic spectra of HD^＋ and HeH^2＋.
基金Supported by the National Natural Science Foundation of China(No.20774077)the Natural Science Foundation of Fujian Province,China(No.E0510003, E0710025)the Project of Science and Technology of Xiamen City,China(No.3502Z20055013)
文摘A series of bowlic cyclotriveratrylenes（CTV） with peripheral groups with different lengths were synthesized.These compounds were investigated by diferential scanning calorimetry and hot stage coupled polarizing microscopy.Several CTV derivatives show thermotropic liquid crystalline properties.The experimental results of their thermotropic liquid crystalline behavior indicate that the clear points,the entropy changes of melting points,the crystallization temperatures,and their entropy changes all exhibited an evident odd-even effect except the melting points,which decreased monotonously with the increase of the length of the alkoxy groups.The parameter values of CTVs with even number carbon atoms were larger than those of CTVs with odd number.When the length of alkoxyl chains was even longer,a monotonous decrease occured.Nevertheless,in the case of the entropy changes of both melting points and crystallization temperatures,the effect was valid for all the six species,and therefore,the whole curves presented as a zig-zag form.
