3,159 research outputs found
Quantum inequalities for the free Rarita-Schwinger fields in flat spacetime
Using the methods developed by Fewster and colleagues, we derive a quantum
inequality for the free massive spin- Rarita-Schwinger fields in
the four dimensional Minkowski spacetime. Our quantum inequality bound for the
Rarita-Schwinger fields is weaker, by a factor of 2, than that for the
spin- Dirac fields. This fact along with other quantum inequalities
obtained by various other authors for the fields of integer spin (bosonic
fields) using similar methods lead us to conjecture that, in the flat
spacetime, separately for bosonic and fermionic fields, the quantum inequality
bound gets weaker as the the number of degrees of freedom of the field
increases. A plausible physical reason might be that the more the number of
field degrees of freedom, the more freedom one has to create negative energy,
therefore, the weaker the quantum inequality bound.Comment: Revtex, 11 pages, to appear in PR
Quantum inequalities in two dimensional curved spacetimes
We generalize a result of Vollick constraining the possible behaviors of the
renormalized expected stress-energy tensor of a free massless scalar field in
two dimensional spacetimes that are globally conformal to Minkowski spacetime.
Vollick derived a lower bound for the energy density measured by a static
observer in a static spacetime, averaged with respect to the observers proper
time by integrating against a smearing function. Here we extend the result to
arbitrary curves in non-static spacetimes. The proof, like Vollick's proof, is
based on conformal transformations and the use of our earlier optimal bound in
flat Minkowski spacetime. The existence of such a quantum inequality was
previously established by Fewster.Comment: revtex 4, 5 pages, no figures, submitted to Phys. Rev. D. Minor
correction
The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables
The temperatures of electrons and ions in the post-shock accretion region of
a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass
flow rates or for sufficiently weak magnetic fields. At lower mass flow rates
or in stronger magnetic fields, efficient cyclotron cooling will cool the
electrons faster than the electrons can cool the ions and a two-temperature
flow will result. Here we investigate the differences in polarized radiation
expected from mCV post-shock accretion columns modeled with one- and
two-temperature hydrodynamics. In an mCV model with one accretion region, a
magnetic field >~30 MG and a specific mass flow rate of ~0.5 g/cm/cm/s, along
with a relatively generic geometric orientation of the system, we find that in
the ultraviolet either a single linear polarization pulse per binary orbit or
two pulses per binary orbit can be expected, depending on the accretion column
hydrodynamic structure (one- or two-temperature) modeled. Under conditions
where the physical flow is two-temperature, one pulse per orbit is predicted
from a single accretion region where a one-temperature model predicts two
pulses. The intensity light curves show similar pulse behavior but there is
very little difference between the circular polarization predictions of one-
and two-temperature models. Such discrepancies indicate that it is important to
model some aspect of two-temperature flow in indirect imaging procedures, like
Stokes imaging, especially at the edges of extended accretion regions, were the
specific mass flow is low, and especially for ultraviolet data.Comment: Accepted for publication in Astrophysics & Space Scienc
Multi-neutron transfer coupling in sub-barrier 32S+90,96Zr fusion reactions
The role of neutron transfers is investigated in the fusion process below the
Coulomb barrier by analyzing 32S+90Zr and 32S+96Zr as benchmark reactions. A
full coupled-channel calculation of the fusion excitation functions has been
performed for both systems by using multi-neutron transfer coupling for the
more neutron-rich reaction. The enhancement of fusion cross sections for
32S+96Zr is well reproduced at sub-barrier energies by NTFus code calculations
including the coupling of the neutron-transfer channels following the Zagrebaev
semiclassical model. We found similar effects for 40Ca+90Zr and 40Ca+96Zr
fusion excitation functions.Comment: Minor corrections, 11 pages, 4 figures, Fusion11 Conference, Saint
Malo, France, 2-6 mai 201
Ion-beam-assisted fabrication and manipulation of metallic nanowires
Metallic nanowires (NWs) are the key performers for future micro/nanodevices. The controlled manoeuvring and integration of such nanoscale entities are essential requirements. Presented is a discussion of a fabrication approach that combines chemical etching and ion beam milling to fabricate metallic NWs. The shape modification of the metallic NWs using ion beam irradiation (bending towards the ion beam side) is investigated. The bending effect of the NWs is observed to be instantaneous and permanent. The ion beam-assisted shape manoeuvre of the metallic structures is studied in the light of ion-induced vacancy formation and reconfiguration of the damaged layers. The manipulation method can be used for fabricating structures of desired shapes and aligning structures at a large scale. The controlled bending method of the metallic NWs also provides an understanding of the strain formation process in nanoscale metals
A comparison of algorithms for generating efficient choice experiments
Stated choice (SC) studies typically rely on the use of an underlying experimental design to construct the hypothetical choice situations shown to respondents. These designs are constructed by the analyst, with several different ways of constructing these designs having been proposed in the past. Recently, there has been a move from so-called orthogonal designs to more efficient designs. Efficient designs optimize the design such that the data will lead to more reliable parameter estimates for the model under consideration. The literature dealing with the generation of efficient designs has examined and largely solved the issue of a requirement for a prior knowledge of the parameter estimates that will be obtained post data collection. However, unlike orthogonal designs, the efficient design methodology requires the evaluation of a number of designs, and hence is computationally expensive to undertake. As such, the literature has suggested and implemented a number of algorithms to locate efficient designs for SC experiments. In this paper, we compare and contrast the performance of these algorithms as well as introduce two new algorithms
Localization of an autonomous mobile robot based on ultrasonic sensory information
Based on ultrasonic sensory information, an approach is proposed for localization of autonomous mobile robot (AMRs). In the proposed method, it will be proven that the combination of three ultrasonic transmitters and two receivers can determine both the position and the orientation of an AMR with respect to a reference frame uniquely. In this manner, since only ultrasonic sensors are used, the proposed method will be highly cost-effective and easy to implement. To show the validity and feasibility of the proposed method, the hardware configuration and a series of experiments will be given for illustration
Inhibitory effect of rhubarb on intestinal α-glucosidase activity in type 1 diabetic rats
Purpose: To investigate the inhibitory effect of rhubarb on α-glucosidase activity in the small intestine of rats with type 1 diabetes.Methods: Type 1 diabetic rat model was established by intraperitoneally injecting 30 male SD rats with 1 % streptozocin (STZ). Rats with fasting blood glucose > 11 mmol/L (24) were used for the study. The rats were randomly divided into three equal groups including control, acarbose and rhubarb groups. ArcaboseÂź (20 mg/kg /day) and rhubarb (100 mg/kg /day) were given by intra-gastric route via insertion of the cannula through the esophagus. Daily fasting blood glucose and daily postprandial glucose levels were assayed for all groups. On day 6, postprandial blood glucose, blood levels of C-peptide and insulin, and intestinal α-glucosidase were also determined.Results: There were no significant differences in levels of C-peptide, insulin and fasting blood glucose between control, AcarboseÂź and rhubarb groups (p > 0.05). However, α-glucosidase activity at 0, 30, 60 and 120 min in the rhubarb group was 1759.2, 1812.8, 1379.8 and 772.1 U, respectively,) while in the AcarboseÂź group it was 178.6, 1260.1, 1126.5, 599.2 U, respectively. α-Glucosidase activity in both groups initially showed an increase (p < 0.05), followed by a decline from 60 to 120 min (p Ë 0.05). After 120 min, α-glucosidase activity in each of the two groups was significantly decreased compared with untreated control (1200 U) (p Ë 0.05).Conclusion: The inhibitory effect of rhubarb on intestinal α-glucosidase activity of Type 1 diabetic rats is comparable to that of ArcaboseÂź.This suggests that this plant may have clinically potent anti-diabetic properties.Keywords: Type 1 diabetes, α-Glucosidase activity, AcarboseÂź, Rhubarb, Postprandial glucose leve
The Intrinsic Dimensionality of Attractiveness: A Study in Face Profiles
The study of human attractiveness with pattern analysis techniques is an emerging research field. One still largely unresolved problem is which are the facial features relevant to attractiveness, how they combine together, and the number of independent parameters required for describing and identifying harmonious faces. In this paper, we present a first study about this problem, applied to face profiles. First, according to several empirical results, we hypothesize the existence of two well separated manifolds of attractive and unattractive face profiles. Then, we analyze with manifold learning techniques their intrinsic dimensionality. Finally, we show that the profile data can be reduced, with various techniques, to the intrinsic dimensions, largely without loosing their ability to discriminate between attractive and unattractive face
Algebraic Quantization, Good Operators and Fractional Quantum Numbers
The problems arising when quantizing systems with periodic boundary
conditions are analysed, in an algebraic (group-) quantization scheme, and the
``failure" of the Ehrenfest theorem is clarified in terms of the already
defined notion of {\it good} (and {\it bad}) operators. The analysis of
``constrained" Heisenberg-Weyl groups according to this quantization scheme
reveals the possibility for new quantum (fractional) numbers extending those
allowed for Chern classes in traditional Geometric Quantization. This study is
illustrated with the examples of the free particle on the circumference and the
charged particle in a homogeneous magnetic field on the torus, both examples
featuring ``anomalous" operators, non-equivalent quantization and the latter,
fractional quantum numbers. These provide the rationale behind flux
quantization in superconducting rings and Fractional Quantum Hall Effect,
respectively.Comment: 29 pages, latex, 1 figure included with EPSF. Revised version with
minor changes intended to clarify notation. Acepted for publication in Comm.
Math. Phy
- âŠ