1,630 research outputs found
Retrieval of interatomic separations of molecules from laser-induced high-order harmonic spectra
We illustrate an iterative method for retrieving the internuclear separations
of N, O and CO molecules using the high-order harmonics generated
from these molecules by intense infrared laser pulses. We show that accurate
results can be retrieved with a small set of harmonics and with one or few
alignment angles of the molecules. For linear molecules the internuclear
separations can also be retrieved from harmonics generated using isotropically
distributed molecules. By extracting the transition dipole moment from the
high-order harmonic spectra, we further demonstrated that it is preferable to
retrieve the interatomic separation iteratively by fitting the extracted dipole
moment. Our results show that time-resolved chemical imaging of molecules using
infrared laser pulses with femtosecond temporal resolutions is possible.Comment: 14 pages, 9 figure
Theoretical analysis of dynamic chemical imaging with lasers using high-order harmonic generation
We report theoretical investigations of the tomographic procedure suggested
by Itatani {\it et al.} [Nature, {\bf 432} 867 (2004)] for reconstructing
highest occupied molecular orbitals (HOMO) using high-order harmonic generation
(HHG). Using the limited range of harmonics from the plateau region, we found
that under the most favorable assumptions, it is still very difficult to obtain
accurate HOMO wavefunction, but the symmetry of the HOMO and the internuclear
separation between the atoms can be accurately extracted, especially when
lasers of longer wavelengths are used to generate the HHG. We also considered
the possible removal or relaxation of the approximations used in the
tomographic method in actual applications. We suggest that for chemical
imaging, in the future it is better to use an iterative method to locate the
positions of atoms in the molecule such that the resulting HHG best fits the
macroscopic HHG data, rather than by the tomographic method.Comment: 13 pages, 14 figure
Improving Heterogeneous Graph Learning with Weighted Mixed-Curvature Product Manifold
In graph representation learning, it is important that the complex geometric
structure of the input graph, e.g. hidden relations among nodes, is well
captured in embedding space. However, standard Euclidean embedding spaces have
a limited capacity in representing graphs of varying structures. A promising
candidate for the faithful embedding of data with varying structure is product
manifolds of component spaces of different geometries (spherical, hyperbolic,
or euclidean). In this paper, we take a closer look at the structure of product
manifold embedding spaces and argue that each component space in a product
contributes differently to expressing structures in the input graph, hence
should be weighted accordingly. This is different from previous works which
consider the roles of different components equally. We then propose
WEIGHTED-PM, a data-driven method for learning embedding of heterogeneous
graphs in weighted product manifolds. Our method utilizes the topological
information of the input graph to automatically determine the weight of each
component in product spaces. Extensive experiments on synthetic and real-world
graph datasets demonstrate that WEIGHTED-PM is capable of learning better graph
representations with lower geometric distortion from input data, and performs
better on multiple downstream tasks, such as word similarity learning, top-
recommendation, and knowledge graph embedding
Retrieval of target structure information from laser-induced photoelectrons by few-cycle bicircular laser fields
Citation: Hoang, V. H., Le, V. H., Lin, C. D., & Le, A. T. (2017). Retrieval of target structure information from laser-induced photoelectrons by few-cycle bicircular laser fields. Physical Review A, 95(3), 6. doi:10.1103/PhysRevA.95.031402By analyzing theoretical results from a numerical solution of the time-dependent Schrodinger equation for atoms in few-cycle bicircular laser pulses, we show that high-energy photoelectron momentum spectra can be used to extract accurate elastic scattering differential cross sections of the target ion with free electrons. We find that the retrieval range for a scattering angle with bicircular pulses is wider than with linearly polarized pulses, although the retrieval method has to be modified to account for different returning directions of the electron in the continuum. This result can be used to extend the range of applicability of ultrafast imaging techniques such as laser-induced electron diffraction and for the accurate characterization of laser pulses
Mycobacterium tuberculosis Beijing genotype emerging in Vietnam.
To assess whether the Mycobacterium tuberculosis Beijing genotype is emerging in Vietnam, we analyzed 563 isolates from new cases by spoligotyping and examined the association between the genotype and age, resistance, and BCG vaccination status. Three hundred one (54%) patients were infected with Beijing genotype strains. The genotype was associated with younger age (and hence with active transmission) and with isoniazid and streptomycin resistance, but not with BCG vaccination
Operator method in solving non-linear equations of the Hartree-Fock type
The operator method is used to construct the solutions of the problem of the
polaron in the strong coupling limit and of the helium atom on the basis of the
Hartree-Fock equation. is obtained for the polaron
ground-state energy. Energies for 2s- and 3s-states are also calculated. The
other excited states are briefly discussed.Comment: 7 page
Working in preventive medicine or not? Flawed perceptions decrease chance of retaining students for the profession
Background: Recruiting and retaining students in preventive medical (PM) specialties has never been easy; one main challenge is how to select appropriate students with proper motivation. Understanding how students perceive PM practice differently from practicing doctors is necessary to guide students, especially for those for whom PM is only a substitute for medicine as their first study preference, properly during their study and, later, the practice of PM. Methods: One thousand three hundred eighty-six PM students in four Vietnamese medical schools and 101 PM doctors filled out a questionnaire about the relevance of 44 characteristics of working in PM. ANOVAs were conducted to define the relationship between students' interest, year of study, willingness to work in PM, and the degree to which students had realistic perceptions of PM practice, compared to doctors' perceptions. Results: Overall, compared to doctors' perceptions, students overestimated the importance of most of the investigated PM practice's characteristics. Moreover, students' perception related to their preference and willing to pursue a career in PM after graduation. In particular, students for whom PM was their first choice had more realistic perceptions of community practice than those who chose PM as their second choice. And, second-choice students had more realistic perceptions than first-choice students in their final years of study, but expected higher work stress in PM practice. Students who were willing to pursue a career in PM rated the importance of community practice higher than those who were not. We also found that students' perception changed during training as senior students had more realistic perceptions of clinical aspects and working stress than junior students, even though they overemphasized the importance of the community aspects of PM practice. Conclusions: To increase the number of students actually entering the PM field after graduation, the flawed perceptions of students about the real working environment of PM doctors should be addressed through vocation-oriented activities in the curriculum targeted on groups of students who are most likely to have unrealistic perceptions. Our findings also have implications for other less attractive primary health care specialties that experience problems with recruiting and retaining students
Groundwater contamination with nitrogenous compounds in Kumamoto Prefecture and Hanoi City : Present conditions and adopted countermeasures
Joint Research on Environmental Science and Technology for the Eart
WATER QUALITY SURVEY OF VIETNAM
Joint Research on Environmental Science and Technology for the Eart
- …