Transformation of alkali and alkaline-earth metals during coal oxy-fuel combustion in the presence of SO_2 and H_2O

The occurrence modes of alkali and alkaline-earth metals（AAEMs） in coal relate to their release behavior and ash formation during combustion. To better understand the transformation of AAEMs,the release behavior of water-soluble,HCl-soluble,HCl-insoluble AAEMs during Shenmu coal（SM coal） oxy-fuel combustion in the presence of SO2 and H2O in a drop-tube reactor was investigated through serial dissolution using H2O and HCl solutions. The results show that the release rates of AAEMs increase with an increase in temperature under the three atmospheres studied. The high release rates of Mg and Ca from SM coal are dependent on the high content of soluble Mg and Ca in SM coal. SO2 inhibits the release rates of AAEMs,while H2O promotes them. The effects of SO2 and H2O on the Na and K species are more evident than those on Mg and Ca species. All three types of AAEMs in coal can volatilize in the gas phase during coal combustion. The W-type AAEMs release excessively,whereas the release rates of I-type AAEMs are relatively lower. Different types of AAEM may interconvert through different pathways under certain conditions. Both SO2 and H2O promote the transformation reactions. The effect of SO2 was related to sulfate formation and the promotion by H2O occurs because of a decrease in the melting point of the solid as well as the reaction of H2O.

Additive effects of alkaline-earth metals and nickel on the performance of Co/γ-Al_2O_3 in methane catalytic partial oxidation

Nano-sized γ-alumina （γ-Al2O3） was first prepared by a precipitation method. Then, active component of cobalt and a series of alkaline- earth metal promoters or nickel （Ni） with different contents were loaded on the γ-Al2O3 support. The catalysts were characterized by N2 adsorption-desorption, X-ray diffraction （XRD） and thermogravimetry analysis （TGA）. The activity and selectivity of the catalysts in catalytic partial oxidation （CPO） of methane have been compared with Co/γ-Al2O3, and it is found that the catalytic activity, selectivity, and stability are enhanced by the addition of alkaline-earth metals and nickel. The optimal loadings of strontium （Sr） and Ni were 6 and 4 wt%, respectively. This finding will be helpful in designing the trimetallic Co-Ni-Sr/γ-Al2O3 catalysts with high performance in CPO of methane

Hydro-geochemistry of groundwater and surface water in Dschang town(West Cameroon):Alkali and alkaline-earth elements ascertain lithological and anthropogenic constraints

The study aims to identify a suitable site for open and bore well in a farmhouseusing ground magnetic survey in south India.It also aims to define depth to granitoid and structural elements which traverse the selected area.Magnetic data(n=84)measured,processed and interpreted as qualitative and quantitatively.The results of total magnetic intensities indicate that the area is composed of linear magnetic lows trending NE-SW direction and circular to semi-circular causative bodies.The magnetic values ranged from-137 nT to 2345 nT with a mean of 465 nT.Reduction to equator shows significant shifting of causative bodies in the southern and northern directions.Analytical signal map shows exact boundary of granitic bodies.Cosine directional filter has brought out structural element trending NE-SW direction.Results of individual profile brought to light structurally weak zone between 90 m and 100 m in all the profile lines.Sudden decrease of magnetic values from 2042 nT to 126 nT noticed in profile line 6 between 20 m and 30 m indicates fault occurrence.Magnetic breaks obtained from these maps were visualized,interpreted and identified two suitable sites for open and bore well.Radially averaged power spectrum estimates depth of shallow and deep sources in 5 m and 50 m,respectively.Euler method has also been applied to estimate depth of granitoid and structural elements using structural indexes 0,1,2,and 3 and found depth ranges from<10 m to>90 m.Study indicates magnetic method is one of the geophysical methods suitable for groundwater exploration and site selection for open and borewells.

Superexchange-mediated magnetization dynamics with ultracold alkaline-earth atoms in an optical lattice

Superexchange and inter-orbital spin-exchange interactions are key ingredients for understanding（orbital） quantum magnetism in strongly correlated systems and have been realized in ultracold atomic gases.Here we study the spin dynamics of ultracold alkaline-earth atoms in an optical lattice when the two exchange interactions coexist.In the superexchange interaction dominating regime,we find that the time-resolved spin imbalance shows a remarkable modulated oscillation,which can be attributed to the interplay between local and nonlocal quantum mechanical exchange mechanisms.Moreover,the filling of the long-lived excited atoms affects the collapse and revival of the magnetization dynamics.These observations can be realized in state-dependent optical lattices combined with the state-of-the-art advances in optical lattice clock spectroscopy.

Blue-emissions Modulated by Packing Forces in Alkaline-earth Metal OrganicFrameworks Based on Thiophene-2,5-dicarboxylic: Structures and Theoretical Calculations

Solvothermal reactions of Ca(NO), Sr(NO)with thiophene-2,5-dicarboxylic in DMF afforded two new inorganic-organic hybrid frameworks, [M(TDC)(DMF)]n(M = Ca(1), Sr(2), TDC = thiophene-2,5-dicarboxylic, DMF = N,N?-dimethylformamide), which have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analysis and IR spectra. Both compounds feature three-dimensional(3D) frameworks based on the versatile coordinated modes(μ-η~2:η~2, μ-η~2:η~1, μ-η~2:η~1) of carboxylic groups in tdc ligands. C–H···S hydrogen bonds and C–H···π interactions contribute to the stabilization of the structures. They exhibit weaker packing force compared with their literature isomers. Consequently, blue and blue/green luminescence of two compounds has been observed. Their luminescence mechanism can be ascribed to ligand-to-metal charge transfer(LMCT) compared with the ligand-centered luminescence in their isomers. Electronic structural calculations illustrate that under the condition of weaker packing forces, larger gaps can be achieved, which facilitate the LMCT. This work suggests that the introduction of S-heteroatom can result in more electrons rich in the metal centers, thus giving rise to metal-involved luminescence.

Alkali/alkaline-earth metal-modified MnO_(x) supported on three-dimensionally ordered macroporous–mesoporous Ti_(x)Si+(1-x)O_(2) catalysts:Preparation and catalytic performance for soot combustion

The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot,which is an important component of atmosphericfine particle emissions.Herein,three-dimensionally ordered macroporous–mesoporous Ti_(x)Si+(1-x)O_(2)(3DOM-m Ti_(x)Si+(1-x)O_(2)) and its supported MnO_(x)catalysts doped with different alkali/alkaline-earth metals (AMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)(A:Li,Na,K,Ru,Cs,Mg,Ca,Sr,Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods,respectively.Physicochemical characterizations of the catalysts were performed using scanning electron microscopy,X-ray diffraction,N_(2)adsorption–desorption,H_(2)temperature-programmed reduction,O_(2)temperature-programmed desorption,NO temperature-programmed oxidation,and Raman spectroscopy techniques;then,we evaluated their catalytic performances for the removal of diesel soot particles.The results show that the 3DOM-m Ti_(0.7)Si_(0.3)O_(2)supports exhibited a well-defined 3DOM-m nanostructure,and AMnO_(x)nanoparticles with 10–50 nm were evenly dispersed on the inner walls of the uniform macropores.In addition,the as-prepared catalysts exhibited good catalytic performance for soot combustion.Among the prepared catalysts,CsMnO_(x)/3DOM-m Ti_(0.7)Si_(0.3)O_(2)had the highest catalytic activity for soot combustion,with T10,T50,and T90(the temperatures corresponding to soot conversion rates of 10%,50%,and 90%) values of 285,355,and 393℃,respectively.The high catalytic activity of the CsMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous–mesoporous structure,as well as to the synergistic effects between Cs and Mn species and between CsMnO_(x)and the Ti_(0.7)Si_(0.3)O_(2)support.

Realization of highly isolated stable few-spin systems based on alkaline-earth fermions

Few-level systems consisting of a certain number of spin states have provided the basis of a wide range of cold atom researches.However,more developments are still needed for better preparation of isolated few-spin systems.In this work,we demonstrate a highly nonlinear spin-discriminating(HNSD)method for isolating an arbitrary few-level manifold out of a larger total number of spin ground states in fermionic alkaline-earth atoms.With this method,we realize large and tunable energy shifts for unwanted spin states while inducing negligible shifts for the spin states of interest,which leads to a highly isolated few-spin system under minimal perturbation.Furthermore,the isolated few-spin system exhibits a long lifetime on the hundred-millisecond scale.Using the HNSD method,we demonstrate a characteristic Rabi oscillation between the two states of an isolated two-spin Fermi gas.Our method has wide applicability for realizing long-lived two-spin or high-spin quantum systems based on alkaline-earth fermions.

Coordination Assembly of Tetrahedral Ti_(4)(embonate)_(6) Cages with Alkaline-Earth Metal Ions

Recently,the tetrahedral Ti_(4)L_(6) cage(L=embonate)has been applied as the starting material to realize coordination assembly with transition and rare-earth ornoble metal ions through a two-step reaction.In this work,by employing the Ti_(4)L_(6) cages to assemble with alkaline-earth metal ions(such as Mg^(2+),Ca^(2+)and Ba^(2+))under different solvothermal conditions,a series of Ti_(4)L_(6)-based structures from simple cages to 1D chain,2D layer and 3D framework have been synthesized and structurally characterized.In addition,thermal stability,phase purity,UV-vis absorption spectrum,the fluorescent and third-order nonlinear-optical properties are also investigated.

Geometry, stability and aromaticity of β-diketiminate-coordinated alkaline-earth compounds

Alkaline-earth(Ae) metals have attracted a wealth of interdependent research from synthetic chemists.In Ae-catalyzed organometallic reactions,β-diketiminate is a typical ligand used to stabilize Ae catalysts by forming six-membered rings comprising Ae metals.Herein,studies focusing on the configuration of β-diketiminate-coordinated Ae compounds observed that the C-C and C-N bonds are homogeneous and unchanged.Furthermore,energetic studies observed that the formation of the Ae-incorporated sixmembered rings results in enhanced stability of>20 kcal/mol.The nucleus-independent chemical shifts,anisotropy of the induced current density,and molecular orbital analyses demonstrated the nonaromaticity of the β-diketiminate-coordinated Ae compounds.The improved stability of these compounds can be explained by the delocalization of the π electrons derived from the β-diketiminate moiety.

Polarons in alkaline-earth-like atoms with multiple background Fermi surfaces

We study the impurity problem in a Fermi gas of 173Yb atoms near an orbital Feshbach resonance （OFR）, where a single moving particle in the 3p0 state interacts with two background Fermi seas of particles in different nuclear states of the ground 1S0 manifold. By employing wave function ansatz to molecule and polaron states, we investigate various properties of the molecule, the attractive polaron, and the repulsive polaron states. In comparison to the case where only one Fermi sea is populated, we find that the presence of an additional Fermi sea acts as an energy shift between the two channels of the OFR. In addition, quantum fluctuations near the Fermi level can also induce sizable effects to various properties of the attractive and repulsive polarons.

Excited-state population distributions of alkaline-earth metal in a hollow cathode lamp

The intensities of fluorescence spectral lines of Ca atoms and Sr atoms in two different hollow cathode lamps （HCLs） are measured by element-balance-detection technology. In the wavelength range of 350–750 nm in the visible spectral region, using the individual strongest line （Ca 422.67 nm, Sr 460.73 nm） as the bench mark, the population ratios between the excited states of Ca atoms and Sr atoms are calculated by rate equations and the spontaneous transition probabilities. The HCLs with populations at excited states can be used to realize the frequency stabilization reference of the laser frequency standard.

Bandgap evolution of Mg_(3)N_(2) under pressure:Experimental and theoretical studies

Wide bandgap semiconductors are crucially significant for optoelectronic and thermoelectric device applications.Metal nitride is a class of semiconductor material with great potential.Under high pressure,the bandgap of magnesium nitride was predicted to grow.Raman spectra,ultra-violet-visible(UV-Vis)absorption spectra,and first-principles calculations were employed in this study to analyze the bandgap evolution of Mg_(3)N_(2).The widening of the bandgap has been first detected experimentally,with the gap increasing from 2.05 eV at 3 GPa to 2.88 eV at 47 GPa.According to the calculation results,the enhanced covalent component is responsible for the bandgap widening.

Rydberg quantum computation with nuclear spins in two-electron neutral atoms

Alkaline-earth-like(AEL)atoms with two valence electrons and a nonzero nuclear spin can be excited to Rydberg state for quantum computing.Typical AEL ground states possess no hyperfine splitting,but unfortunately a GHz-scale splitting seems necessary for Rydberg excitation.Though strong magnetic fields can induce a GHz-scale splitting,weak fields are desirable to avoid noise in experiments.Here,we provide two solutions to this outstanding challenge with realistic data of well-studied AEL isotopes.In the first theory,the two nuclear spin qubit states∣0〉and∣1〉are excited to Rydberg states∣r〉with detuningΔand 0,respectively,where a MHz-scale detuningΔarises from a weak magnetic field on the order of 1 G.With a proper ratio betweenΔandΩ,the qubit state∣1〉can be fully excited to the Rydberg state while∣0〉remains there.In the second theory,we show that by choosing appropriate intermediate states a two-photon Rydberg excitation can proceed with only one nuclear spin qubit state.The second theory is applicable whatever the magnitude of the magnetic field is.These theories bring a versatile means for quantum computation by combining the broad applicability of Rydberg blockade and the incomparable advantages of nuclear-spin quantum memory in two-electron neutral atoms.

A New Tubular Borate Built by[B_(14)O_(24)(OH)_(6)]^(12-) Cluster Units

Anew mixed alkali and alkaline-earth metal borate Na4Ca2[B14O22(OH)6]·2H2O(1) has been made under a mild solvothermal condition and characterized by single-crystal X-ray diffraction, infrared(IR) spectroscopy, UV-Vis diffuse reflectance spectroscopy, powder X-ray diffraction and thermogravimetric analysis, respectively. Compound 1 features a 1D tube based on[B14O24(OH)6]12-({B14}-1) oxo-boron clusters. Such a tube built by {B14}-1 units has been discovered for the first time in borate system. These tubes are arranged orderly to generate 2D layers and a further 3D supramolecular network through hydrogen bond interactions. UV-Vis diffuse reflectance spectrum reveals that compound 1 is a wide band-gap semiconductor and has potential application in UV region.

Fine controllable blue emission and its mechanism in Ce^(3+)-doped orthosilicate solid solution phosphors for different plant growths

The designed Ce^3＋-doped alkaline-earth silicate phosphors CamSr2 m-nBanSiO4：Ce^3＋,Li^＋ （CSBS：Ce^3＋） were synthesized by a high temperature solid-state reaction. The crystal field splitting and the centroid shift from the flee ion energy of 5d configuration were approximated from the spectrum for Ca2SiO4, Sr2SiO4 and Ba2SiO4 phosphors. The single-phase purity was checked by means of X-ray diffraction. Here, when the doped concentration of Ca2. is less than 80% （m 〈 1.6）, we report the structural phase transformation from monoclinic system [3-Ca2Si04 to orthorhombic system α′-Ca2SiO4. The phosphors excited by near-ultraviolet （NUV） light at wavelengths ranging from 200 to 400 nm demonstrate a broad asymmetric blue emission band. The emission peak wavelength redshifts firstly from 417 nm of Ca2SiO4 to 438 nm of Sro.3Cal.6SiO4, and then blueshifts to 411 nm of Sr2SiO4, and the end of 401 nm of Ba2SiOa. These results indicate that the tunable blue-emission of the phosphors can he realized through changing the solid solution components, which has a potential use as a blue component for fabricated precision modulation LEDs light sources and auxiliaries of SSC plastics films for different plant growths. We discuss in detail the possible mechanism and energy diagram of the tunable blue luminescence in CamSr2-M-nBaNSiO4：Ce^3＋.Li^＋ phosphors.