20,065 research outputs found
Semiclassical theory of spectral line shapes. II. Applications to CO, HCl, and OCS, broadened by inert gases
The semiclassical theory of spectral line broadening developed in the previous paper of this series is used to calculate the half‐widths and shifts of nonoverlapping rotational spectral lines of CO, HCl, and OCS, broadened by inert gases. Comparisons are made with the available experimental data and with related theoretical analyses, and reasonable agreement is obtained. The method used applies both to fairly quantum systems as well as to the relatively classical ones. A symmetrized semiclassical expression for Wigner 6‐j symbols is given and applied
REGULATORY APPROVAL OF NEW MEDICAL DEVICES: A CROSS SECTIONAL STUDY
Objective To investigate the regulatory approval of new medical devices. Design Cross sectional study of new medical devices reported in the biomedical literature. Data sources PubMed was searched between 1 January 2000 and 31 December 2004 to identify clinical studies of new medical devices. The search was carried out during this period to allow time for regulatory approval. Eligibility criteria for study selection Articles were included if they reported a clinical study of a new medical device and there was no evidence of a previous clinical study in the literature. We defined a medical device according to the US Food and Drug Administration as an “instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or other similar or related article.” Main outcome measures Type of device, target specialty, and involvement of academia or of industry for each clinical study. The FDA medical databases were then searched for clearance or approval relevant to the device. Results 5574 titles and abstracts were screened, 493 full text articles assessed for eligibility, and 218 clinical studies of new medical devices included. In all, 99/218 (45%) of the devices described in clinical studies ultimately received regulatory clearance or approval. These included 510(k) clearance for devices determined to be “substantially equivalent” to another legally marketed device (78/99; 79%), premarket approval for high risk devices (17/99; 17%), and others (4/99; 4%). Of these, 43 devices (43/99; 43%) were actually cleared or approved before a clinical study was published. Conclusions We identified a multitude of new medical devices in clinical studies, almost half of which received regulatory clearance or approval. The 510(k) pathway was most commonly used, and clearance often preceded the first published clinical study
Uniform semiclassical theory of avoided crossings
A voided crossings influence spectra and intramolecular redistribution of energy. A semiclassical theory
of these avoided crossings shows that when primitive semiclassical eigenvalues are plotted vs a parameter
in the Hamiltonian they cross instead of avoiding each other. The trajectories for each are connected by a
classically forbidden path. To obtain the avoided crossing behavior, a uniform semiclassical theory of
avoided crossings is presented in this article for the case where that behavior is generated by a classical
resonance. A low order perturbation theory expression is used as the basis for a functional form for the
treatment. The parameters in the expression are evaluated from canonical invariants (phase integrals)
obtained from classical trajectory data. The results are compared with quantum mechanical results for
the splitting, and reasonable agreement is obtained. Other advantages of the uniform method are
described
Toward quantum simulations of biological information flow
Recent advances in the spectroscopy of biomolecules have highlighted the
possibility of quantum coherence playing an active role in biological energy
transport. The revelation that quantum coherence can survive in the hot and wet
environment of biology has generated a lively debate across both the physics
and biology communities. In particular, it remains unclear to what extent
non-trivial quantum effects are utilised in biology and what advantage, if any,
they afford. We propose an analogue quantum simulator, based on currently
available techniques in ultra-cold atom physics, to study a model of energy and
electron transport based on the Holstein Hamiltonian By simulating the salient
aspects of a biological system in a tunable laboratory setup, we hope to gain
insight into the validity of several theoretical models of biological quantum
transport in a variety of relevant parameter regimes.Comment: 8 Pages, 2 Figures, Non-technical contributing article for the
Interface Focus Theme Issue `Computability and the Turning centenary'.
Interface Focus
http://rsfs.royalsocietypublishing.org/content/early/2012/03/22/rsfs.2011.0109.shor
Wide-angle perfect absorber/thermal emitter in the THz regime
We show that a perfect absorber/thermal emitter exhibiting an absorption peak
of 99.9% can be achieved in metallic nanostructures that can be easily
fabricated. The very high absorption is maintained for large angles with a
minimal shift in the center frequency and can be tuned throughout the visible
and near-infrared regime by scaling the nanostructure dimensions. The stability
of the spectral features at high temperatures is tested by simulations using a
range of material parameters.Comment: Submitted to Phys. Rev. Let
Multiple cooperating manipulators: The case of kinematically redundant arms
Existing work concerning two or more manipulators simultaneously grasping and transferring a common load is continued and extended. Specifically considered is the case of one or more arms being kinematically redundant. Some existing results in the modeling and control of single redundant arms and multiple manipulators are reviewed. The cooperating situation is modeled in terms of a set of coordinates representing object motion and internal object squeezing. Nominal trajectories in these coordinates are produced via actuator load distribution algorithms introduced previously. A controller is developed to track these desired object trajectories while making use of the kinematic redundancy to additionally aid the cooperation and coordination of the system. It is shown how the existence of kinematic redundancy within the system may be used to enhance the degree of cooperation achievable
Sensing human hand motions for controlling dexterous robots
The Dexterous Hand Master (DHM) system is designed to control dexterous robot hands such as the UTAH/MIT and Stanford/JPL hands. It is the first commercially available device which makes it possible to accurately and confortably track the complex motion of the human finger joints. The DHM is adaptable to a wide variety of human hand sizes and shapes, throughout their full range of motion
Instantons on sine-cones over Sasakian manifolds
We investigate instantons on sine-cones over Sasaki-Einstein and 3-Sasakian
manifolds. It is shown that these conical Einstein manifolds are K"ahler with
torsion (KT) manifolds admitting Hermitian connections with totally
antisymmetric torsion. Furthermore, a deformation of the metric on the
sine-cone over 3-Sasakian manifolds allows one to introduce a hyper-K"ahler
with torsion (HKT) structure. In the large-volume limit these KT and HKT spaces
become Calabi-Yau and hyper-K"ahler conifolds, respectively. We construct gauge
connections on complex vector bundles over conical KT and HKT manifolds which
solve the instanton equations for Yang-Mills fields in higher dimensions.Comment: 1+15 pages, 2 figure
Fast Single-Charge Sensing with an rf Quantum Point Contact
We report high-bandwidth charge sensing measurements using a GaAs quantum
point contact embedded in a radio frequency impedance matching circuit
(rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to
charge, we demonstrate a conductance sensitivity of 5x10^(-6) e^(2)/h Hz^(-1/2)
with a bandwidth of 8 MHz. Single-shot readout of a proximal few-electron
double quantum dot is investigated in a mode where the rf-QPC back-action is
rapidly switched.Comment: related papers available at http://marcuslab.harvard.ed
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