8,950 research outputs found
Evaluation of the importance of spin-orbit couplings in the nonadiabatic quantum dynamics with quantum fidelity and with its efficient "on-the-fly" ab initio semiclassical approximation
We propose to measure the importance of spin-orbit couplings (SOCs) in the
nonadiabatic molecular quantum dynamics rigorously with quantum fidelity. To
make the criterion practical, quantum fidelity is estimated efficiently with
the multiple-surface dephasing representation (MSDR). The MSDR is a
semiclassical method that includes nuclear quantum effects through interference
of mixed quantum-classical trajectories without the need for the Hessian of
potential energy surfaces. Two variants of the MSDR are studied, in which the
nuclei are propagated either with the fewest-switches surface hopping or with
the locally mean field dynamics. The fidelity criterion and MSDR are first
tested on one-dimensional model systems amenable to numerically exact quantum
dynamics. Then, the MSDR is combined with "on-the-fly" computed electronic
structure to measure the importance of SOCs and nonadiabatic couplings (NACs)
in the photoisomerization dynamics of CH2NH2+ considering 20 electronic states
and in the collision of F + H2 considering six electronic states.Comment: 9 pages, 3 figures, submitted to J. Chem. Phy
Labour process theory and critical management studies
Labour Process Theory (LPT) is conventionally and rightly listed as one of the analytical resources for Critical Management Studies (CMS). Yet, the relationships between the two have been, in the words of a classic of the former, a contested terrain. This is hardly surprising. Even if we set aside the inevitable multiplicity of perspectives, there is a tension in potential objects of analysis. Before CMS burst on to the scene, LPT was being criticised at its peak of influence in the 1980s for paying too much attention to management and too little to capital(ism) and labour. This was sometimes attributed to the location of many of the protagonists (in the UK at least) in business schools, but was, more likely a reflection of wider theoretical and ideological divides
Optimising and automating the choice of search strings when investigating possible plagiarism
This paper describes how to optimise the use of Internet search engines when investigating a document for possible non-original content. Services such as Turnitin do not guarantee to identify all non-original content, leading tutors to have to conduct manual searches when suspicion of non-originality remains. Previous studies have suggested that the investigator should manually select memorable phrases from the paper and submit them to a general search engine. The studies in this paper demonstrate that selecting phrases at random is just as effective. Several corpora of documents were obtained from a number of different academic areas, and several phrases were obtained from each. Strings, of increasing length starting with a single word, from these phrases were submitted to specialised and general search engines and the number of hits recorded. A common finding of these searches was that, in almost all cases, strings of six words were sufficiently distinct to uniquely identify the document that the string was taken from. One consequence of this is that totally automated tools are possible for this search-engine based non-originality detection technique
Bifurcation in Rotational Spectra of Nonlinear AB Molecules
A classical microscopic theory of rovibrational motion at high angular
momenta in symmetrical non-linear molecules AB is derived within the
framework of small oscillations near the stationary states of a rotating
molecule. The full-dimensional analysis including stretching vibrations has
confirmed the existence of the bifurcation predicted previously by means of the
rigid-bender model. The formation of fourfold energy clusters has already been
experimentally verified for HSe and it has been demonstrated in
fully-dimensional quantum mechanical calculations using the MORBID computer
program. We show in the present work that apart from the level clustering, the
bifurcation produces physically important effects including molecular
symmetry-breaking and a transition from the normal mode to the local mode limit
for the stretching vibrations due to rovibrational interaction. The application
of the present theory with realistic molecular potentials to the HTe,
HSe and HS hydrides results in predictions of the bifurcation points
very close to those calculated previously. However for the lighter HO
molecule we find that the bifurcation occurs at higher values of the total
angular momentum than obtained in previous estimations. The present work shows
it to be very unlikely that the bifurcation in HO will lead to clustering
of energy levels. This result is in agreement with recent variational
calculations.Comment: latex, 19 pages including 2 figures provided as *.uu fil
Association of molecules using a resonantly modulated magnetic field
We study the process of associating molecules from atomic gases using a
magnetic field modulation that is resonant with the molecular binding energy.
We show that maximal conversion is obtained by optimising the amplitude and
frequency of the modulation for the particular temperature and density of the
gas. For small modulation amplitudes, resonant coupling of an unbound atom pair
to a molecule occurs at a modulation frequency corresponding to the sum of the
molecular binding energy and the relative kinetic energy of the atom pair. An
atom pair with an off-resonant energy has a probability of association which
oscillates with a frequency and time-varying amplitude which are primarily
dependent on its detuning. Increasing the amplitude of the modulation tends to
result in less energetic atom pairs being resonantly coupled to the molecular
state, and also alters the dynamics of the transfer from continuum states with
off-resonant energies. This leads to maxima and minima in the total conversion
from the gas as a function of the modulation amplitude. Increasing the
temperature of the gas leads to an increase in the modulation frequency
providing the best fit to the thermal distribution, and weakens the resonant
frequency dependence of the conversion. Mean-field effects can alter the
optimal modulation frequency and lead to the excitation of higher modes. Our
simulations predict that resonant association can be effective for binding
energies of order MHz.Comment: 8 pages latex, figures revised, references updated and typos
correcte
Recommended from our members
Development of a Virtual Laparoscopic Trainer using Accelerometer Augmented Tools to Assess Performance in Surgical training
Previous research suggests that virtual reality (VR) may supplement conventional training in laparoscopy. It may prove useful in the selection of surgical trainees in terms of their dexterity and spatial awareness skills in the near future. Current VR training solutions provide levels of realism and in some instances, haptic feedback, but they are cumbersome by being tethered and not ergonomically close to the actual surgical instruments for weight and freedom of use factors. In addition, they are expensive hence making them less accessible to departments than conventional box trainers. The box trainers in comparison, although more economical, lack tangible feedback and realism for handling delicate tissue structures. We have previously reported on the development of a modified digitally enhanced surgical instrument for laparoscopic training, named the Parkar Tool. This tool contains wireless accelerometer and gyroscopic sensors integrated into actual laparoscopic instruments. By design, it alleviates the need for both tethered and physically different shaped tools thereby enhancing the realism when performing surgical procedures. Additionally the software (Valhalla) has the ability to digitally record surgical motions, thereby enabling it to remotely capture surgical training data to analyse and objectively evaluate performance. We have adapted and further developed our initial single training tool method as used with a laparoscopic pyloromyotomy scenario, to an enhanced method using multiple Parkar wireless tools simultaneously, for use in several different case scenarios. This allows the use and measurement of right and left handed dexterity with the benefit of using several tasks of differing complexity. The development of a 3D tissue-surface deformations solution written in OpenGL gives us several different virtual surgical training scenario approximations to use with the instruments. The trainee can start with learning simple tasks e.g. incising tissue, grasping, squeezing and stretching tissue, to more complex procedures such as suturing, herniotomies, bowel anastomoses, as well as the original pyloromyotomy as used in the first model
Sewing sound quantum flesh onto classical bones
Semiclassical transformation theory implies an integral representation for
stationary-state wave functions in terms of angle-action variables
(). It is a particular solution of Schr\"{o}dinger's time-independent
equation when terms of order and higher are omitted, but the
pre-exponential factor in the integrand of this integral
representation does not possess the correct dependence on . The origin of
the problem is identified: the standard unitarity condition invoked in
semiclassical transformation theory does not fix adequately in a
factor which is a function of the action written in terms of and
. A prescription for an improved choice of this factor, based on
succesfully reproducing the leading behaviour of wave functions in the vicinity
of potential minima, is outlined. Exact evaluation of the modified integral
representation via the Residue Theorem is possible. It yields wave functions
which are not, in general, orthogonal. However, closed-form results obtained
after Gram-Schmidt orthogonalization bear a striking resemblance to the exact
analytical expressions for the stationary-state wave functions of the various
potential models considered (namely, a P\"{o}schl-Teller oscillator and the
Morse oscillator).Comment: RevTeX4, 6 page
Visualising Java Coupling and Fault Proneness
In this paper, a tool is described for visualising the Coupling Between Objects (CBO) metric for Java systems, decomposing it into coupling collaborators and using colour to denote the object-oriented mechanisms at work for each couple. The resulting visualisation is also envisaged to be useful for general program comprehension and is integrated into Java development in the Eclipse IDE. Evidence is also given that the visualisation may help detect classes tending to be less fault-prone than would be expected from inspection of their CBO values alone
- …