We propose an ion-trap scheme for one-step generation of a special configuration of W-class state which has recently been shown to be better than canonical W states for several quantum-information processing tasks. We...We propose an ion-trap scheme for one-step generation of a special configuration of W-class state which has recently been shown to be better than canonical W states for several quantum-information processing tasks. We also present a method for one-step realization of a nontrivial collective operation which can transform a canonical W state into a fully separable state. Such a transformation plays a key role in recently proposed quantum protocols. The operation speed in our schemes increases with the number of qubits. This is contrary to usual entanglement generation and quantum manipulation schemes which take more and more time with the increase of the number of qubits.展开更多
After deregulating the purine and riboflavin synthesis in the Gram-positive bacterium Bacillus subtilis,it is critical to amplify riboflavin operon with appropriate dosage in the host strain for remarkable increase of...After deregulating the purine and riboflavin synthesis in the Gram-positive bacterium Bacillus subtilis,it is critical to amplify riboflavin operon with appropriate dosage in the host strain for remarkable increase of riboflavin production.Bacillus subtilis RH13, a riboflavin-producing strain, was selected as host strain in the construction of engineering strains by protoplast fusion. The integrative plasmid pRB63 and autonomous plasmid pRB49, pRB62 containing riboflavin operon of B.subtilis 24 were constructed and transformed into the host strain respectively. Increasing one operon copy in B.subtilis RH13 results in about 0.4 g/L improvement in riboflavin yield and the appropriate number of operon copies was about 7—8. Amplifying more riboflavin operons is of no use for further improvement of yield of riboflavin. Furthermore, excessive operon dosage results in metabolic unbalance and is fatal to the host cells producing riboflavin.展开更多
We have theoretically analyzed the quasibound states in a Mraphene quantum dot （GO, D） with a magnetic flux -φ in the centre. It is shown that the two-fold time reversal degeneracy is broken and the quasibound stat...We have theoretically analyzed the quasibound states in a Mraphene quantum dot （GO, D） with a magnetic flux -φ in the centre. It is shown that the two-fold time reversal degeneracy is broken and the quasibound states of GQD with positive^negative angular momentum shifted upwards/downwards with increasing the magnetic flux. The variation of the quasibound energy depends linearly on the magnetic flux, which is quite different from the parabolic relationship for SchrSdinger electrons. The GQD＇s quasibound states spectrum shows an obvious Aharonov-Bohm （AB） oscillations with the magnetic flux. It is also shown that the quasibound state with energy equal to the barrier height becomes a bound state completely confined in GQD.展开更多
The security of the multiparty quantum secret sharing protocol proposed by Gao [G.Gao,Commun.Theor.Phys.52 (2009) 421] is analyzed.It is shown that this protocol is vulnerable since the agents' imperfectencryption...The security of the multiparty quantum secret sharing protocol proposed by Gao [G.Gao,Commun.Theor.Phys.52 (2009) 421] is analyzed.It is shown that this protocol is vulnerable since the agents' imperfectencryption scheme can be attacked by a powerful participant.We introduce a attack strategy called participant forciblemanipulation and analyze the information leakage in this protocol under this attack.At last,we give an improved versionof the original protocol.The improved protocol is robust and has the same efficiency as the original one.展开更多
OBJECTIVE: To examine the feasibility of linking operons in tandem to enhance expression of heterologous genes in Escherichia coli (E. coli) and clarify the potential control mechanism of the total plasmid DNA amount ...OBJECTIVE: To examine the feasibility of linking operons in tandem to enhance expression of heterologous genes in Escherichia coli (E. coli) and clarify the potential control mechanism of the total plasmid DNA amount in each host cell. METHODS: Two series of expression plasmids, CW11 and CW12, containing 1 to 4 and 1 to 3 heterologous gene operon(s) respectively, were constructed. The molecular size of the CW11 series varied from 5.47 kb to 12.26 kb in 2.25 kb increments. The CW12 series varied from 5.40 kb to 9.72 kb in 2.16 kb increments. The expression level of desired protein was assayed by SDS-PAGE and laser density scanning. Plasmid copy number was determined by incorporation with (3)H-thymidine ((3)H-TdR). RESULTS: No influence of the tandem-joined operons on host growth and plasmid stability was observed. Upon induction, the desired protein accumulations in the CW11 series were 44.9% +/- 3.9%, 51.3% +/- 4.1%, 54.8% +/- 3.3% and 58.2% +/- 3.4% of total cell protein. In the CW12 series, the yields were 32.2% +/- 5.0%, 42.8% +/- 4.1% and 46.9% +/- 4.0% of total cell protein. As size increased, the plasmid copy number decreased, but target gene dosage increased significantly (P 0.05) and restricted to some extent. CONCLUSIONS: Increasing the target gene dosage by tandem linking of operons may enhance the expression level of a desired protein. Although the size (kb) and the copy number of each plasmid are negatively interrelated, for certain plasmids in each series, their total DNA amount per cell seems to be a restricted constant for specific E. coli strains under identical incubation condition.展开更多
The availability of a large number of sequenced bacterial genomes facilitates in-depth studies about why genes(operons)in a bacterial genome are globally organized the way they are.We have previously discovered that(t...The availability of a large number of sequenced bacterial genomes facilitates in-depth studies about why genes(operons)in a bacterial genome are globally organized the way they are.We have previously discovered that(the relative)transcription-activation frequencies among different biological pathways encoded in a genome have a dominating role in the global arrangement of operons.One complicating factor in such a study is that some operons may be involved in multiple pathways with different activation frequencies.A quantitative model has been developed that captures this information,which tends to be minimized by the current global arrangement of operons in a bacterial(and archaeal)genome compared to possible alternative arrangements.A study is carried out here using this model on a collection of 52 closely related Escherichia coli genomes,which revealed interesting new insights about how bacterial genomes evolve to optimally adapt to their environments through adjusting the(relative)genomic locations of the encoding operons of biological pathways once their utilization and hence transcription activation frequencies change,to maintain the above energy-efficiency property.More specifically we observed that it is the frequencies of the transcription activation of pathways relative to those of the other encoded pathways in an organism as well as the variation in the activation frequencies of a specific pathway across the related genomes that play a key role in the observed commonalities and differences in the genomic organizations of genes(and operons)encoding specific pathways across different genomes.展开更多
The system of electrons on liquid helium is an interesting candidate to implement quantum computation, due to the long coherence times of the qubits encoded by the electronic spins. In order to implement the quantum l...The system of electrons on liquid helium is an interesting candidate to implement quantum computation, due to the long coherence times of the qubits encoded by the electronic spins. In order to implement the quantum logic operations between the spins, we propose here a configuration, similarly to the cooled ions in a trap, to couple the distant electrons via manipulating their center of mass （CM） vibrations. First, we show that the electrons could be confined in a common harmonic oscillator potential by using an electrostatic field. Then, with a single current pulse （applied on the micro-electrode below the liquid helium） the distant electronic spins can be coupled simultaneously to the CM mode. Finally, by adiabatically eliminating the CM mode, effective interaction between the distant spins is induced for implementing the desired quantum computing.展开更多
Above-threshold ionizations of rare gas atoms excited by polarized femtosecond laser pulses are investigated.The photoelectron momentum spectra are obtained applying the strong-field approximation(SFA) theory.It is fo...Above-threshold ionizations of rare gas atoms excited by polarized femtosecond laser pulses are investigated.The photoelectron momentum spectra are obtained applying the strong-field approximation(SFA) theory.It is found that,distribution of the emitted photoelectrons varies with different polarizations of laser pulses.We have interpreted the relationship between the observed distribution and the laser polarization taking advantage of tunneling ionization theory and simple-man model.The polarization sensitivity indicates that one can easily manipulate the photoelectron distribution by controlling the polarization of the exciting pulse.展开更多
Manipulation of spontaneous emission from an atom confined in three kinds of modified reservoirs has been investigated by means of an elliptically polarized laser field. Some interesting phenomena such as the multi-pe...Manipulation of spontaneous emission from an atom confined in three kinds of modified reservoirs has been investigated by means of an elliptically polarized laser field. Some interesting phenomena such as the multi-peak structure, extreme spectral narrowing, and cancellation of spontaneous emission can be observed by adjusting controllable system parameters. Moreover, these phenomena depend on the constructive or destructive quantum interference between multiple decay channels and which can be changed appreciably by varying the phase difference between the two circularly polarized components of the probe field. These results demonstrate the importance of an elliptially polarized laser field in controlling the spontaneous emission and its potential applications in high-precision spectroscopy.展开更多
基金Supported by the Natural Science Foundation of Hunan Province under Grant No.06JJ50015
文摘We propose an ion-trap scheme for one-step generation of a special configuration of W-class state which has recently been shown to be better than canonical W states for several quantum-information processing tasks. We also present a method for one-step realization of a nontrivial collective operation which can transform a canonical W state into a fully separable state. Such a transformation plays a key role in recently proposed quantum protocols. The operation speed in our schemes increases with the number of qubits. This is contrary to usual entanglement generation and quantum manipulation schemes which take more and more time with the increase of the number of qubits.
文摘After deregulating the purine and riboflavin synthesis in the Gram-positive bacterium Bacillus subtilis,it is critical to amplify riboflavin operon with appropriate dosage in the host strain for remarkable increase of riboflavin production.Bacillus subtilis RH13, a riboflavin-producing strain, was selected as host strain in the construction of engineering strains by protoplast fusion. The integrative plasmid pRB63 and autonomous plasmid pRB49, pRB62 containing riboflavin operon of B.subtilis 24 were constructed and transformed into the host strain respectively. Increasing one operon copy in B.subtilis RH13 results in about 0.4 g/L improvement in riboflavin yield and the appropriate number of operon copies was about 7—8. Amplifying more riboflavin operons is of no use for further improvement of yield of riboflavin. Furthermore, excessive operon dosage results in metabolic unbalance and is fatal to the host cells producing riboflavin.
基金Support by National Science Foundation of China under Grant Nos. 60776067 and 10974011
文摘We have theoretically analyzed the quasibound states in a Mraphene quantum dot （GO, D） with a magnetic flux -φ in the centre. It is shown that the two-fold time reversal degeneracy is broken and the quasibound states of GQD with positive^negative angular momentum shifted upwards/downwards with increasing the magnetic flux. The variation of the quasibound energy depends linearly on the magnetic flux, which is quite different from the parabolic relationship for SchrSdinger electrons. The GQD＇s quasibound states spectrum shows an obvious Aharonov-Bohm （AB） oscillations with the magnetic flux. It is also shown that the quasibound state with energy equal to the barrier height becomes a bound state completely confined in GQD.
基金Supported by National Natural Science Foundation of China under Grant Nos.60873191,60903152,60821001Specialized Research Fund for the Doctoral Program of High Education under Grant Nos.200800131016 and 20090005110010+2 种基金Beijing Nova Program under Grant No.2008B51Key Project of Chinese Ministry of Education under Grant No.109014Beijing Natural Science Foundation under Grant Nos.4072020 and 4102055
文摘The security of the multiparty quantum secret sharing protocol proposed by Gao [G.Gao,Commun.Theor.Phys.52 (2009) 421] is analyzed.It is shown that this protocol is vulnerable since the agents' imperfectencryption scheme can be attacked by a powerful participant.We introduce a attack strategy called participant forciblemanipulation and analyze the information leakage in this protocol under this attack.At last,we give an improved versionof the original protocol.The improved protocol is robust and has the same efficiency as the original one.
基金ThisstudywassupportedbyagrantfromtheNationalHighTechnologyResearchandDevelopmentProgram (No .10 2 0 8 0 20 2)
文摘OBJECTIVE: To examine the feasibility of linking operons in tandem to enhance expression of heterologous genes in Escherichia coli (E. coli) and clarify the potential control mechanism of the total plasmid DNA amount in each host cell. METHODS: Two series of expression plasmids, CW11 and CW12, containing 1 to 4 and 1 to 3 heterologous gene operon(s) respectively, were constructed. The molecular size of the CW11 series varied from 5.47 kb to 12.26 kb in 2.25 kb increments. The CW12 series varied from 5.40 kb to 9.72 kb in 2.16 kb increments. The expression level of desired protein was assayed by SDS-PAGE and laser density scanning. Plasmid copy number was determined by incorporation with (3)H-thymidine ((3)H-TdR). RESULTS: No influence of the tandem-joined operons on host growth and plasmid stability was observed. Upon induction, the desired protein accumulations in the CW11 series were 44.9% +/- 3.9%, 51.3% +/- 4.1%, 54.8% +/- 3.3% and 58.2% +/- 3.4% of total cell protein. In the CW12 series, the yields were 32.2% +/- 5.0%, 42.8% +/- 4.1% and 46.9% +/- 4.0% of total cell protein. As size increased, the plasmid copy number decreased, but target gene dosage increased significantly (P 0.05) and restricted to some extent. CONCLUSIONS: Increasing the target gene dosage by tandem linking of operons may enhance the expression level of a desired protein. Although the size (kb) and the copy number of each plasmid are negatively interrelated, for certain plasmids in each series, their total DNA amount per cell seems to be a restricted constant for specific E. coli strains under identical incubation condition.
基金supported in part by National Science Foundation (#NSF DEB-0830024 and NSF MCB-0958172)the US Department of Energy’s BioEnergy Science Center grant through the Office of Biological and Environmental Research+1 种基金The BioEnergy Science Center is a US Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of ScienceFunding for open access charge: US Department of Energy’s BioEnergy Science Center
文摘The availability of a large number of sequenced bacterial genomes facilitates in-depth studies about why genes(operons)in a bacterial genome are globally organized the way they are.We have previously discovered that(the relative)transcription-activation frequencies among different biological pathways encoded in a genome have a dominating role in the global arrangement of operons.One complicating factor in such a study is that some operons may be involved in multiple pathways with different activation frequencies.A quantitative model has been developed that captures this information,which tends to be minimized by the current global arrangement of operons in a bacterial(and archaeal)genome compared to possible alternative arrangements.A study is carried out here using this model on a collection of 52 closely related Escherichia coli genomes,which revealed interesting new insights about how bacterial genomes evolve to optimally adapt to their environments through adjusting the(relative)genomic locations of the encoding operons of biological pathways once their utilization and hence transcription activation frequencies change,to maintain the above energy-efficiency property.More specifically we observed that it is the frequencies of the transcription activation of pathways relative to those of the other encoded pathways in an organism as well as the variation in the activation frequencies of a specific pathway across the related genomes that play a key role in the observed commonalities and differences in the genomic organizations of genes(and operons)encoding specific pathways across different genomes.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11204249,11174373the National Fundamental Research Program of China under Grant No.2010CB923104
文摘The system of electrons on liquid helium is an interesting candidate to implement quantum computation, due to the long coherence times of the qubits encoded by the electronic spins. In order to implement the quantum logic operations between the spins, we propose here a configuration, similarly to the cooled ions in a trap, to couple the distant electrons via manipulating their center of mass （CM） vibrations. First, we show that the electrons could be confined in a common harmonic oscillator potential by using an electrostatic field. Then, with a single current pulse （applied on the micro-electrode below the liquid helium） the distant electronic spins can be coupled simultaneously to the CM mode. Finally, by adiabatically eliminating the CM mode, effective interaction between the distant spins is induced for implementing the desired quantum computing.
基金Supported by the National Natural Science Foundation of China under Grant No. 11104210
文摘Above-threshold ionizations of rare gas atoms excited by polarized femtosecond laser pulses are investigated.The photoelectron momentum spectra are obtained applying the strong-field approximation(SFA) theory.It is found that,distribution of the emitted photoelectrons varies with different polarizations of laser pulses.We have interpreted the relationship between the observed distribution and the laser polarization taking advantage of tunneling ionization theory and simple-man model.The polarization sensitivity indicates that one can easily manipulate the photoelectron distribution by controlling the polarization of the exciting pulse.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11004069 and 91021011the Doctoral Foundation of the Ministry of Education of China under Grant No.20100142120081the National Basic Research Program of China under Grant No.2012CB922103
文摘Manipulation of spontaneous emission from an atom confined in three kinds of modified reservoirs has been investigated by means of an elliptically polarized laser field. Some interesting phenomena such as the multi-peak structure, extreme spectral narrowing, and cancellation of spontaneous emission can be observed by adjusting controllable system parameters. Moreover, these phenomena depend on the constructive or destructive quantum interference between multiple decay channels and which can be changed appreciably by varying the phase difference between the two circularly polarized components of the probe field. These results demonstrate the importance of an elliptially polarized laser field in controlling the spontaneous emission and its potential applications in high-precision spectroscopy.
