221,263 research outputs found
Partition functions and double-trace deformations in AdS/CFT
We study the effect of a relevant double-trace deformation on the partition
function (and conformal anomaly) of a CFT at large N and its dual picture in
AdS. Three complementary previous results are brought into full agreement with
each other: bulk and boundary computations, as well as their formal identity.
We show the exact equality between the dimensionally regularized partition
functions or, equivalently, fluctuational determinants involved. A series of
results then follows: (i) equality between the renormalized partition functions
for all d; (ii) for all even d, correction to the conformal anomaly; (iii) for
even d, the mapping entails a mixing of UV and IR effects on the same side
(bulk) of the duality, with no precedent in the leading order computations; and
finally, (iv) a subtle relation between overall coefficients, volume
renormalization and IR-UV connection. All in all, we get a clean test of the
AdS/CFT correspondence beyond the classical SUGRA approximation in the bulk and
at subleading O(1) order in the large-N expansion on the boundary.Comment: 18 pages, uses JHEP3.cls. Published JHEP versio
A & B model approaches to surface operators and Toda theories
It has recently been argued by Alday et al that the inclusion of surface
operators in 4d N=2 SU(2) quiver gauge theories should correspond to insertions
of certain degenerate operators in the dual Liouville theory. So far only the
insertion of a single surface operator has been treated (in a semi-classical
limit). In this paper we study and generalise this proposal. Our approach
relies on the use of topological string theory techniques. On the B-model side
we show that the effects of multiple surface operator insertions in 4d N=2
gauge theories can be calculated using the B-model topological recursion
method, valid beyond the semi-classical limit. On the mirror A-model side we
find by explicit computations that the 5d lift of the SU(N) gauge theory
partition function in the presence of (one or many) surface operators is equal
to an A-model topological string partition function with the insertion of (one
or many) toric branes. This is in agreement with an earlier proposal by Gukov.
Our A-model results were motivated by and agree with what one obtains by
combining the AGT conjecture with the dual interpretation in terms of
degenerate operators. The topological string theory approach also opens up new
possibilities in the study of 2d Toda field theories.Comment: 43 pages. v2: Added references, including a reference to unpublished
work by S.Gukov; minor changes and clarifications
Perturbative and non-perturbative aspects of the two-dimensional string/Yang-Mills correspondence
It is known that YM_2 with gauge group SU(N) is equivalent to a string theory
with coupling g_s=1/N, order by order in the 1/N expansion. We show how this
results can be obtained from the bosonization of the fermionic formulation of
YM_2, improving on results in the literature, and we examine a number of
non-perturbative aspects of this string/YM correspondence. We find
contributions to the YM_2 partition function of order exp{-kA/(\pi\alpha' g_s)}
with k an integer and A the area of the target space, which would correspond,
in the string interpretation, to D1-branes. Effects which could be interpreted
as D0-branes are instead stricly absent, suggesting a non-perturbative
structure typical of type 0B string theories. We discuss effects from the YM
side that are interpreted in terms of the stringy exclusion principle of
Maldacena and Strominger. We also find numerically an interesting phase
structure, with a region where YM_2 is described by a perturbative string
theory separated from a region where it is described by a topological string
theory.Comment: 24 pages, 5 figure
Path integral evaluation of equilibrium isotope effects
A general and rigorous methodology to compute the quantum equilibrium isotope
effect is described. Unlike standard approaches, ours does not assume
separability of rotational and vibrational motions and does not make the
harmonic approximation for vibrations or rigid rotor approximation for the
rotations. In particular, zero point energy and anharmonicity effects are
described correctly quantum mechanically. The approach is based on the
thermodynamic integration with respect to the mass of isotopes and on the
Feynman path integral representation of the partition function. An efficient
estimator for the derivative of free energy is used whose statistical error is
independent of the number of imaginary time slices in the path integral,
speeding up calculations by a factor of 60 at 500 K. We describe the
implementation of the methodology in the molecular dynamics package Amber 10.
The method is tested on three [1,5] sigmatropic hydrogen shift reactions.
Because of the computational expense, we use ab initio potentials to evaluate
the equilibrium isotope effects within the harmonic approximation, and then the
path integral method together with semiempirical potentials to evaluate the
anharmonicity corrections. Our calculations show that the anharmonicity effects
amount up to 30% of the symmetry reduced reaction free energy. The numerical
results are compared with recent experiments of Doering and coworkers,
confirming the accuracy of the most recent measurement on
2,4,6,7,9-pentamethyl-5-(5,5-H)methylene-11,11a-dihydro-12H-naphthacene
as well as concerns about compromised accuracy, due to side reactions, of
another measurement on
2-methyl-10-(10,10-H)methylenebicyclo[4.4.0]dec-1-ene.Comment: 14 pages, 8 figures, 6 table
Comparative study of the interaction of CHAPS and Triton X-100 with the erythrocyte membrane
AbstractThe zwitterionic detergent CHAPS, a derivative of the bile salts, is widely used in membrane protein solubilization. It is a âfacialâ detergent, having a hydrophilic side and a hydrophobic back. The objective of this work is to characterize the interaction of CHAPS with a cell membrane. To this aim, erythrocytes were incubated with a wide range of detergent concentrations in order to determine CHAPS partition behavior, and its effects on membrane lipid order, hemolytic effects, and the solubilization of membrane phospholipids and cholesterol. The results were compared with those obtained with the nonionic detergent Triton X-100. It was found that CHAPS has a low affinity for the erythrocyte membrane (partition coefficient K=0.06mMâ1), and at sub-hemolytic concentrations it causes little effect on membrane lipid order. CHAPS hemolysis and phospholipid solubilization are closely correlated. On the other side, binding of Triton X-100 disorders the membrane at all levels, and has independent mechanisms for hemolysis and solubilization. Differential behavior was observed in the solubilization of phospholipids and cholesterol. Thus, the detergent resistant membranes (DRM) obtained with the two detergents will have different composition. The behaviors of the two detergents are related to the differences in their molecular structures, suggesting that CHAPS does not penetrate the lipid bilayer but binds in a flat position on the erythrocyte surface, both in intact and cholesterol depleted erythrocytes. A relevant result for Triton X-100 is that hemolysis is not directly correlated with the solubilization of membrane lipids, as it is usually assumed
Sound Absorbent And Damping Rate of The Natural Composites Design
This research was conducted to determine the sound attenuation level of  composite. The composite used in this study iscompound Kalimantan sawdust and pineapple leaf fiber. The research objective was to determine the damping rate of composites (fine Kalimantan sawdust and compound of coarse Kalimantan sawdust with pineapple leaf fiber), so it can be used as an alternative sound absorbent material. The composite testing process uses a Sounds Level Meter by adjusting the frequency of the sound source. The space partition is a composite, measured the value of sound intensity at a certain distance, then given a partition, the sound intensity is again measured with the same distance. The results of the absorption coefficient of pineapple leaf fiber composite and red meranti wood sawdust can be used as an alternative sound absorbing material besides glass wool so that it can minimize side effects for public health. ©2018 JNSMR UIN Walisongo. All rights reserved
Using zeta-potential measurements to quantify peptide partition to lipid membranes
© The Author(s) 2011. This article is published with open access at Springerlink.com.Open Access: This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.Many cellular phenomena occur on the biomembranes. There are plenty of molecules (natural or xenobiotics) that interact directly or partially with the cell membrane. Biomolecules, such as several peptides (e.g., antimicrobial peptides) and proteins, exert their effects at the cell membrane level. This feature makes necessary investigating their interactions with lipids to clarify their mechanisms of action and side effects necessary. The determination of molecular lipid/water partition constants (Kp) is frequently used to quantify the extension of the interaction. The determination of this parameter has been achieved by using different methodologies, such as UV-Vis absorption spectrophotometry, fluorescence spectroscopy and ζ-potential measurements. In this work, we derived and tested a mathematical model to determine the Kp from ζ-potential data. The values obtained with this method were compared with those obtained by fluorescence spectroscopy, which is a regular technique used to quantify the interaction of intrinsically fluorescent peptides with selected biomembrane model systems. Two antimicrobial peptides (BP100 and pepR) were evaluated by this new method. The results obtained by this new methodology show that ζ-potential is a powerful technique to quantify peptide/lipid interactions of a wide variety of charged molecules, overcoming some of the limitations inherent to other techniques, such as the need for fluorescent labeling.This work was partially supported by project PTDC/QUI/ 69937/2006 from Fundação para a CiĂȘncia e Tecnologia-MinistĂ©rio da CiĂȘncia, Tecnologia e Ensino Superior (FCT-MCTES, Portugal), and by Fundação Calouste Gulbenkian (Portugal). JMF and MMD also thank FCT-MCTES for grants IMM/BT/37-2010 and SFRH/BD/41750/2007, respectively
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Memory-Based High-Level Synthesis Optimizations Security Exploration on the Power Side-Channel
High-level synthesis (HLS) allows hardware designers to think algorithmically and not worry about low-level, cycle-by-cycle details. This provides the ability to quickly explore the architectural design space and tradeoffs between resource utilization and performance. Unfortunately, security evaluation is not a standard part of the HLS design flow. In this article, we aim to understand the effects of memory-based HLS optimizations on power side-channel leakage. We use Xilinx Vivado HLS to develop different cryptographic cores, implement them on a Spartan-6 FPGA, and collect power traces. We evaluate the designs with respect to resource utilization, performance, and information leakage through power consumption. We have two important observations and contributions. First, the choice of resource optimization directive results in different levels of side-channel vulnerabilities. Second, the partitioning optimization directive can greatly compromise the hardware cryptographic system through power side-channel leakage due to the deployment of memory control logic. We describe an evaluation procedure for power side-channel leakage and use it to make best-effort recommendations about how to design more secure architectures in the cryptographic domain
Exact results on ABJ theory and the refined topological string
We study the partition function of the ABJ theory, which is the N=6
superconformal Chern-Simons matter theory with gauge group U(N)xU(N+M) and
Chern-Simons levels (k,-k). We exactly compute the ABJ partition function on a
three sphere for various k, M and N via the Fermi gas approach. By using these
exact data, we show that the ABJ partition function is completely determined by
the refined topological string on local P^1 x P^1, including membrane instanton
effects in the M-theory dual.Comment: 24+29 pages, 4 figures; v2:minor improvement
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