1,737 research outputs found
Constructive Field Theory and Applications: Perspectives and Open Problems
In this paper we review many interesting open problems in mathematical
physics which may be attacked with the help of tools from constructive field
theory. They could give work for future mathematical physicists trained with
the constructive methods well within the 21st century
Interrelationship of Major Topological Indices Evidenced by Clustering
This study examines the mutual relatedness of 318 major topological indices (TIs) for three sets of molecules: (i) a set of 139 hydrocarbons, (ii) a diverse set of 1029 compounds and (iii) a diverse set of 2887 compounds. The TIs included in this study are those that have been frequently used in the characterization of structure and QSAR/ QSPR studies. After variable reduction based on the elimination of TIs for which all values were zero and those that were completely correlated with another TI, a variable clustering technique was used to cluster the TIs which resulted in 16, 37 and 56 clusters, respectively, for the three data sets mentioned above. Analysis of the correspondence among the clusters derived from the three groups of chemicals has been carried out in an effort to understand the dimensionality of the structure spaces derived for the three different sets of chemicals and the structural aspects characterized by the various TIs
Can adding Ephedrine to Admixture of Propofol & Lidocaine Overcome Propofol Associated Hemodynamic Changes and Injection Pain?
Purpose: There are numerous studies researching ways to alleviate propofol injection pain. In this study, we evaluated and compared the use of propofol-lidocaine admixture vs propofol-lidocaine combined with ephedrine, on vascular pain and hemodynamic changes associated propofol. Methods: This double-blinded, prospective, randomised study was performed on 100 patients with ASA I-II who were divided into two group. The first received admixture consisting of 20 mg of lidocaine and propofol 1% 20 ml (Group L), and the other received admixture consisting of 20 mcg ephedrine, 20 mg lidocaine and propofol 1% 20 ml (Group LE). Baseline and after induction heart rate, mean arterial pressure and rate pressure product (RPP) were recorded per minute. Vascular pain were evaluated with verbal rating scale. Results: Data of 40 patients in group L and 39 patients in Group LE were evaluated in the study. The incidence of pain in group L was 90%, it was 38.4% for Group LE. Mild pain was observed significantly more in Group L when compared to Group LE (p<0.05). Average blood pressure and RPP immediately after induction and 1 min after intubation were significantly higher in group LE compared to group L (p<0.05). Heart rate was higher in Group LE immediately after induction and at initially 4 minutes after intubation. Conclusion: Our study has demonstrated significant decrease in rate of vascular pain and increased hemodynamic stability in patients receiving 20 mg ephedrine added to 20 ml % 1 propofol and 20 mg lidocaine admixture when compared to those who only received the lidocaine-propofol admixtur
Strong, Ultra-narrow Peaks of Longitudinal and Hall Resistances in the Regime of Breakdown of the Quantum Hall Effect
With unusually slow and high-resolution sweeps of magnetic field, strong,
ultra-narrow (width down to ) resistance peaks are observed in
the regime of breakdown of the quantum Hall effect. The peaks are dependent on
the directions and even the history of magnetic field sweeps, indicating the
involvement of a very slow physical process. Such a process and the sharp peaks
are, however, not predicted by existing theories. We also find a clear
connection between the resistance peaks and nuclear spin polarization.Comment: 5 pages with 3 figures. To appear in PR
Absence of Scaling in the Integer Quantum Hall Effect
We have studied the conductivity peak in the transition region between the
two lowest integer Quantum Hall states using transmission measurements of edge
magnetoplasmons. The width of the transition region is found to increase
linearly with frequency but remains finite when extrapolated to zero frequency
and temperature. Contrary to prevalent theoretical pictures, our data does not
show the scaling characteristics of critical phenomena.These results suggest
that a different mechanism governs the transition in our experiment.Comment: Minor changes and new references include
On Renormalization Group Flows and Polymer Algebras
In this talk methods for a rigorous control of the renormalization group (RG)
flow of field theories are discussed. The RG equations involve the flow of an
infinite number of local partition functions. By the method of exact
beta-function the RG equations are reduced to flow equations of a finite number
of coupling constants. Generating functions of Greens functions are expressed
by polymer activities. Polymer activities are useful for solving the large
volume and large field problem in field theory. The RG flow of the polymer
activities is studied by the introduction of polymer algebras. The definition
of products and recursive functions replaces cluster expansion techniques.
Norms of these products and recursive functions are basic tools and simplify a
RG analysis for field theories. The methods will be discussed at examples of
the -model, the -model and hierarchical scalar field
theory (infrared fixed points).Comment: 32 pages, LaTeX, MS-TPI-94-12, Talk presented at the conference
``Constructive Results in Field Theory, Statistical Mechanics and Condensed
Matter Physics'', 25-27 July 1994, Palaiseau, Franc
Field-induced breakdown of the quantum Hall effect
A numerical analysis is made of the breakdown of the quantum Hall effect
caused by the Hall electric field in competition with disorder. It turns out
that in the regime of dense impurities, in particular, the number of localized
states decreases exponentially with the Hall field, with its dependence on the
magnetic and electric field summarized in a simple scaling law. The physical
picture underlying the scaling law is clarified. This intra-subband process,
the competition of the Hall field with disorder, leads to critical breakdown
fields of magnitude of a few hundred V/cm, consistent with observations, and
accounts for their magnetic-field dependence \propto B^{3/2} observed
experimentally. Some testable consequences of the scaling law are discussed.Comment: 7 pages, Revtex, 3 figures, to appear in Phys. Rev.
Information inequalities and Generalized Graph Entropies
In this article, we discuss the problem of establishing relations between
information measures assessed for network structures. Two types of entropy
based measures namely, the Shannon entropy and its generalization, the
R\'{e}nyi entropy have been considered for this study. Our main results involve
establishing formal relationship, in the form of implicit inequalities, between
these two kinds of measures when defined for graphs. Further, we also state and
prove inequalities connecting the classical partition-based graph entropies and
the functional-based entropy measures. In addition, several explicit
inequalities are derived for special classes of graphs.Comment: A preliminary version. To be submitted to a journa
Quantum Hall fluctuations and evidence for charging in the quantum Hall effect
We find that mesoscopic conductance fluctuations in the quantum Hall regime
in silicon MOSFETs display simple and striking patterns. The fluctuations fall
into distinct groups which move along lines parallel to loci of integer filling
factor in the gate voltage-magnetic field plane. Also, a relationship appears
between the fluctuations on quantum Hall transitions and those found at low
densities in zero magnetic field. These phenomena are most naturally attributed
to charging effects. We argue that they are the first unambiguous manifestation
of interactions in dc transport in the integer quantum Hall effect.Comment: 4 pages RevTeX including 4 postscript bitmapped figure
High Magnetic Field Microwave Conductivity of 2D Electrons in an Array of Antidots
We measure the high magnetic field () microwave conductivity,
Re, of a high mobility 2D electron system containing an antidot
array. Re vs frequency () increases strongly in the regime of
the fractional quantum Hall effect series, with Landau filling .
At microwave , Re vs exhibits a broad peak centered around
. On the peak, the 10 GHz Re can exceed its dc-limit
value by a factor of 5. This enhanced microwave conductivity is unobservable
for temperature K, and grows more pronounced as is
decreased. The effect may be due to excitations supported by the antidot edges,
but different from the well-known edge magnetoplasmons.Comment: 4 pages, 3 figures, revtex
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