547 research outputs found
On some point groups
In this note, we indicate the coincidence as abstract groups of some point groups which belong to different molecular orbitals. This elucidates somewhat vague presentation in many existing textbooks on molecular orbitals, thus abridging between group theory and quantum chemistry
High-order harmonic generation in graphene: Nonlinear coupling of intraband and interband transitions
We investigate high-order harmonic generation (HHG) in graphene with a quantum master equation approach. The simulations reproduce the observed enhancement in HHG in graphene under elliptically polarized light [N. Yoshikawa et al., Science 356, 736 (2017)]. On the basis of a microscopic decomposition of the emitted high-order harmonics, we find that the enhancement in HHG originates from an intricate nonlinear coupling between the intraband and interband transitions that are respectively induced by perpendicular electric field components of the elliptically polarized light. Furthermore, we reveal that contributions from different excitation channels destructively interfere with each other. This finding suggests a path to potentially enhance the HHG by blocking a part of the channels and canceling the destructive interference through band-gap or chemical potential manipulation
Intersubband electronic Raman scattering in narrow GaAs single quantum wells dominated by single-particle excitations
We measured resonant Raman scattering by intersubband electronic excitations
in GaAs/AlAs single quantum wells (QWs) with well widths ranging from 8.5 to 18
nm. In narrow (less than 10 nm) QWs with sufficiently high electron
concentrations, only single-particle excitations (SPEs) were observed in
intersubband Raman scattering, which was confirmed by the well-width dependence
of Raman spectra. We found characteristic variations in Raman shift and line
shape for SPEs with incident photon energy in the narrow QWs.Comment: 5 pages including 4 figure
A new method to establish the rational extent of hepatic resection for advanced gallbladder cancer using dye injection through the cystic artery
BackgroundHepatic resection has been indicated to eliminate cancer at the surgical margin in cases of advanced gallbladder carcinoma, but there is considerable controversy about the reasonable extent of liver resection. A new on‐table dye injection technique has been introduced to determine the venous drainage of the gallbladder and ascertain the amount of liver to remove.MethodsIn four hepatic resections for pT2 gallbladder cancer, indocyanine green solution (25 mg/20 ml) was injected over a period of 30 seconds through the cystic artery. The stained area of the liver surface was completely resected, maintaining a margin of at least 2 cm from the gallbladder.ResultsThe entire serosal surface of the gallbladder takes on a light green stain immediately after dye injection, and then the liver surface around the gallbladder gradually becomes stained with a clear demarcation line. The distance between the demarcation line and the gallbladder ranged from 1.0 to 5.0 cm. The extent of the stained area differed from one individual to another. Histopathological examination of resected liver specimens revealed that one of the four resected livers had micrometastasis in the portal area 27 mm from the gallbladder wall and there were no cancer cells at the surgical margins. No recurrence has been seen in any of our 4 patients at 16–26 months after operation.DiscussionThe dye injection method is useful in determining the appropriate extent of hepatic resection for advanced gallbladder cancer, as it is possible to determine the necessary and sufficient amount of liver parenchyma that should be removed according to the perfusion area of the cystic veins in each individual patient
Size-controlled quantum dots reveal the impact of intraband transitions on high-order harmonic generation in solids
Since the discovery of high-order harmonic generation (HHG) in solids1,2,3, much effort has been devoted to understand its generation mechanism and both inter- and intraband transitions are known to be essential1,2,3,4,5,6,7,8,9,10. However, intraband transitions are affected by the electronic structure of a solid, and how they contribute to nonlinear carrier generation and HHG remains an open question. Here we use mid-infrared laser pulses to study HHG in CdSe and CdS quantum dots, where quantum confinement can be used to control the intraband transitions. We find that both HHG intensity per excited volume and generated carrier density increase when the average quantum dot size is increased from about 2 to 3 nm. We show that the reduction in sub-bandgap energy in larger quantum dots enhances intraband transitions, and this—in turn—increases the rate of photocarrier injection by coupling with interband transitions, resulting in enhanced HHG
Optical echo in photonic crystals
The dynamics of photonic wavepacket in the effective oscillator potential is
studied. The oscillator potential is constructed on a base of one dimensional
photonic crystal with a period of unit cell adiabatically varied in space. The
structure has a locally equidistant discrete spectrum. This leads to an echo
effect, i.e. the periodical reconstruction of the packet shape. The effect can
be observed in a nonlinear response of the system. Numerical estimations for
porous-silicon based structures are presented for femtosecond Ti:Sapphire laser
pump.Comment: 4 page
Belief and Intention towards Design Ethics among Design Undergraduates in Malaysian Higher Education Institutions
This paper reports on the findings of a study by design graduates on their belief and intention on ethical issues in the creative design industry. The study was conducted at two universities (University A and University B) in Malaysia, which included 120 undergraduates in design. A survey was conducted in which a questionnaire was distributed among respondents to determine their degree of agreement with respect to each argument in the questionnaire. The results of the data showed that the belief and intention of design graduates towards design ethics is poor, with the exception of the respondents of University A who have strong belief towards social, environmental and sustainability issues. These results indicate that a well-structured model of design ethics education and effective teaching mechanism for design ethics education should be in place. These would have an impact on students’ belief and intention towards design ethics. As such, the research results serve as a cornerstone from which the current practice of teaching and learning of design ethics education can be more critically examined, so that more changes can be made to the existing curriculum that can help to develop designers with ethical characteristics
Optical properties of structurally-relaxed Si/SiO superlattices: the role of bonding at interfaces
We have constructed microscopic, structurally-relaxed atomistic models of
Si/SiO superlattices. The structural distortion and oxidation-state
characteristics of the interface Si atoms are examined in detail. The role
played by the interface Si suboxides in raising the band gap and producing
dispersionless energy bands is established. The suboxide atoms are shown to
generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and
optical-absorption calculations at the Fermi Golden rule level are used to
demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue
shift in the spectrum, and (c) an enhancement of the absorption intensity in
the threshold-energy region. Some aspects of this behaviour appear not only in
the symmetry direction associated with the superlattice axis, but also in the
orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO
superlattices show clear optical enhancement and a shift of the optical
spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B
Surface-Related States in Oxidized Silicon Nanocrystals Enhance Carrier Relaxation and Inhibit Auger Recombination
Physics of the Riemann Hypothesis
Physicists become acquainted with special functions early in their studies.
Consider our perennial model, the harmonic oscillator, for which we need
Hermite functions, or the Laguerre functions in quantum mechanics. Here we
choose a particular number theoretical function, the Riemann zeta function and
examine its influence in the realm of physics and also how physics may be
suggestive for the resolution of one of mathematics' most famous unconfirmed
conjectures, the Riemann Hypothesis. Does physics hold an essential key to the
solution for this more than hundred-year-old problem? In this work we examine
numerous models from different branches of physics, from classical mechanics to
statistical physics, where this function plays an integral role. We also see
how this function is related to quantum chaos and how its pole-structure
encodes when particles can undergo Bose-Einstein condensation at low
temperature. Throughout these examinations we highlight how physics can perhaps
shed light on the Riemann Hypothesis. Naturally, our aim could not be to be
comprehensive, rather we focus on the major models and aim to give an informed
starting point for the interested Reader.Comment: 27 pages, 9 figure
- …