22,176 research outputs found
Linear scaling calculation of maximally-localized Wannier functions with atomic basis set
We have developed a linear scaling algorithm for calculating
maximally-localized Wannier functions (MLWFs) using atomic orbital basis. An
O(N) ground state calculation is carried out to get the density matrix (DM).
Through a projection of the DM onto atomic orbitals and a subsequent O(N)
orthogonalization, we obtain initial orthogonal localized orbitals. These
orbitals can be maximally localized in linear scaling by simple Jacobi sweeps.
Our O(N) method is validated by applying it to water molecule and wurtzite ZnO.
The linear scaling behavior of the new method is demonstrated by computing the
MLWFs of boron nitride nanotubes.Comment: J. Chem. Phys. in press (2006
Coherent control of plasma dynamics
Coherent control of a system involves steering an interaction to a final
coherent state by controlling the phase of an applied field. Plasmas support
coherent wave structures that can be generated by intense laser fields. Here,
we demonstrate the coherent control of plasma dynamics in a laser wakefield
electron acceleration experiment. A genetic algorithm is implemented using a
deformable mirror with the electron beam signal as feedback, which allows a
heuristic search for the optimal wavefront under laser-plasma conditions that
is not known a priori. We are able to improve both the electron beam charge and
angular distribution by an order of magnitude. These improvements do not simply
correlate with having the `best' focal spot, since the highest quality vacuum
focal spot produces a greatly inferior electron beam, but instead correspond to
the particular laser phase that steers the plasma wave to a final state with
optimal accelerating fields
Quantum Dot in Z-shaped Graphene Nanoribbon
Stimulated by recent advances in isolating graphene, we discovered that
quantum dot can be trapped in Z-shaped graphene nanoribbon junciton. The
topological structure of the junction can confine electronic states completely.
By varying junction length, we can alter the spatial confinement and the number
of discrete levels within the junction. In addition, quantum dot can be
realized regardless of substrate induced static disorder or irregular edges of
the junction. This device can be used to easily design quantum dot devices.
This platform can also be used to design zero-dimensional functional nanoscale
electronic devices using graphene ribbons.Comment: 4 pages, 3 figure
cDNA, genomic sequence cloning and overexpression of ribosomal protein S16 gene (RPS16) from the Giant Panda
RPS16 of eukaryote is a component of the 40S small ribosomal subunit encoded by RPS16 gene and is also a homolog of prokaryotic RPS9. The cDNA and genomic sequence of RPS16 was cloned successfully for the first time from the Giant Panda (Ailuropoda melanoleuca) using reverse transcription-polymerase chain reaction (RT-PCR) technology and Touchdown-PCR, respectively, which were both sequenced and analyzed preliminarily. The cDNA of the RPS16 gene was overexpressed in Escherichia coli BL21. The length of cDNA fragment cloned is 448 bp containing an open reading frame of 441 bp encoding 146 amino acids and the length of the genomic sequence is 2510 bp, containing five exons and four introns. Alignment analysis indicates that the nucleotide sequence share a high homology with those of Bos taurus, Homo sapiens, Mus musculus, Rattus norvegicus and Danio rerio by 95.46, 92.97, 89.80, 89.80 and 82.54%, respectively. The deduced amino acid sequence is entirely identical compared with the first four animals and share a high homology with that of D. rerio by 96.58%. Topology prediction shows that there is one cAMP- and cGMP-dependent protein kinase phosphorylation site, three protein kinase C phosphorylation sites, one casein kinase II phosphorylation site, two N-myristoylation sites, one amidation site and one ribosomal protein S9 signature in the RPS16 protein of the Giant Panda . The RPS16 gene can be readily expressed in E. coli and it fused with the N-terminally GST-tagged protein which gave rise to the accumulation of an expected 20.095 kDa polypeptide, in good agreement with the predicted molecular weight. The expression product obtained could be used for purification and further study of its function
Levinson's theorem for the Schr\"{o}dinger equation in two dimensions
Levinson's theorem for the Schr\"{o}dinger equation with a cylindrically
symmetric potential in two dimensions is re-established by the Sturm-Liouville
theorem. The critical case, where the Schr\"{o}dinger equation has a finite
zero-energy solution, is analyzed in detail. It is shown that, in comparison
with Levinson's theorem in non-critical case, the half bound state for
wave, in which the wave function for the zero-energy solution does not decay
fast enough at infinity to be square integrable, will cause the phase shift of
wave at zero energy to increase an additional .Comment: Latex 11 pages, no figure and accepted by P.R.A (in August); Email:
[email protected], [email protected]
Distinguishing left- and right-handed molecules by two-step coherent pulses
Chiral molecules with broken parity symmetries can be modeled as quantum
systems with cyclic-transition structures. By using these novel properties, we
design two-step laser pulses to distinguish left- and right-handed molecules
from the enantiomers. After the applied pulse drivings, one kind chiral
molecules are trapped in coherent population trapping state, while the other
ones are pumped to the highest states for ionizations. Then, different chiral
molecules can be separated.Comment: 11 pages, 3 figures
- …