1,278 research outputs found
Matrix models on the fuzzy sphere
Field theory on a fuzzy noncommutative sphere can be considered as a
particular matrix approximation of field theory on the standard commutative
sphere. We investigate from this point of view the scalar theory. We
demonstrate that the UV/IR mixing problems of this theory are localized to the
tadpole diagrams and can be removed by an appropiate (fuzzy) normal ordering of
the vertex. The perturbative expansion of this theory reduces in the
commutative limit to that on the commutative sphere.Comment: 6 pages, LaTeX2e, Talk given at the NATO Advanced Research Workshop
on Confiment, Topology, and other Non-Perturbative Aspects of QCD, Stara
Lesna, Slovakia, Jan. 21-27, 200
Comment on ``A new efficient method for calculating perturbative energies using functions which are not square integrable'': regularization and justification
The method recently proposed by Skala and Cizek for calculating perturbation
energies in a strict sense is ambiguous because it is expressed as a ratio of
two quantities which are separately divergent. Even though this ratio comes out
finite and gives the correct perturbation energies, the calculational process
must be regularized to be justified. We examine one possible method of
regularization and show that the proposed method gives traditional quantum
mechanics results.Comment: 6 pages in REVTeX, no figure
Ultrafast Raman laser mode-locked by nanotubes
We demonstrate passive mode-locking of a Raman fiber laser using a nanotube-based saturable absorber coupled to a net normal dispersion cavity. This generates highly chirped 500 ps pulses. These are then compressed down to 2 ps , with 1.4 kW peak power, making it a simple wavelength-versatile source for various applications
Recommended from our members
Mechanisms Underlying Age- and Performance-related Differences in Working Memory
This study took advantage of the subsecond temporal resolution of ERPs to investigate mechanisms underlying age- and performance-related differences in working memory. Young and old subjects participated in a verbal n-back task with three levels of difficulty. Each group was divided into high and low performers based on accuracy under the 2-back condition. Both old subjects and low-performing young subjects exhibited impairments in preliminary mismatch/match detection operations (indexed by the anterior N2 component). This may have undermined the quality of information available for the subsequent decision-making process (indexed by the P3 component), necessitating the appropriation of more resources. Additional anterior and right hemisphere activity was recruited by old subjects. Neural efficiency and the capacity to allocate more resources to decision-making differed between high and low performers in both age groups. Under low demand conditions, high performers executed the task utilizing fewer resources than low performers (indexed by the P3 amplitude). As task requirements increased, high-performing young and old subjects were able to appropriate additional resources to decision-making, whereas their low-performing counterparts allocated fewer resources. Higher task demands increased utilization of processing capacity for operations other than decision-making (e.g., sustained attention) that depend upon a shared pool of limited resources. As demands increased, all groups allocated additional resources to the process of sustaining attention (indexed by the posterior slow wave). Demands appeared to have exceeded capacity in low performers, leading to a reduction of resources available to the decision-making process, which likely contributed to a decline in performance
Phosphorylation of ribosomal protein S6 confers PARP inhibitor resistance in BRCA1-deficient cancers
Inhibition of poly(ADP-ribose) polymerase (PARP) is a promising therapeutic strategy for BRCA1 deficient cancers, however, the development of drug resistance limits clinical efficacy. Previously we found that the BRCA1-AKT1 pathway contributes to tumorigenesis and that the AKT1/mTOR is a novel therapeutic target for BRCA1-deficient cancers. Here, we report that phosphorylation of ribosomal protein S6, a mTOR downstream effector, is greatly increased in BRCA1 deficient cells resistant to PARP inhibition. Phosphorylation of S6 is associated with DNA damage and repair signaling during PARP inhibitor treatment. In BRCA1 deficient cells, expression of S6 lacking all five phosphorylatable sites renders the cells sensitive to PARP inhibitor and increases DNA damage signals. In addition, the S6 mutations reduce tumor formation induced by Brca1-deficiency in mice. Inhibition of S6 phosphorylation by rapamycin restores PARP sensitivity to resistant cells. Combined treatment with rapamycin and PARP inhibitor effectively suppresses BRCA1-deficient tumor growth in mice. These results provide evidence for a novel mechanism by which BRCA1 deficient cancers acquire drug resistance and suggest a new therapeutic strategy to circumvent resistance
"Forget" the Forget Gate: Estimating Anomalies in Videos using Self-contained Long Short-Term Memory Networks
Abnormal event detection is a challenging task that requires effectively
handling intricate features of appearance and motion. In this paper, we present
an approach of detecting anomalies in videos by learning a novel LSTM based
self-contained network on normal dense optical flow. Due to their sigmoid
implementations, standard LSTM's forget gate is susceptible to overlooking and
dismissing relevant content in long sequence tasks like abnormality detection.
The forget gate mitigates participation of previous hidden state for
computation of cell state prioritizing current input. In addition, the
hyperbolic tangent activation of standard LSTMs sacrifices performance when a
network gets deeper. To tackle these two limitations, we introduce a bi-gated,
light LSTM cell by discarding the forget gate and introducing sigmoid
activation. Specifically, the LSTM architecture we come up with fully sustains
content from previous hidden state thereby enabling the trained model to be
robust and make context-independent decision during evaluation. Removing the
forget gate results in a simplified and undemanding LSTM cell with improved
performance effectiveness and computational efficiency. Empirical evaluations
show that the proposed bi-gated LSTM based network outperforms various LSTM
based models verifying its effectiveness for abnormality detection and
generalization tasks on CUHK Avenue and UCSD datasets.Comment: 16 pages, 7 figures, Computer Graphics International (CGI) 202
BMN operators with vector impurities, Z_2 symmetry and pp-waves
We calculate the coefficients of three-point functions of BMN operators with
two vector impurities. We find that these coefficients can be obtained from
those of the three-point functions of scalar BMN operators by interchanging the
coefficient for the symmetric-traceless representation with the coefficient for
the singlet. We conclude that the Z_2 symmetry of the pp-wave string theory is
not manifest at the level of field theory three-point correlators.Comment: 25 pages, 7 figures. v1: A reference and a footnote added; v2: New
contributions found, Z_2 symmetry lost in 3-point function
Local Commutativity and Causality in Interacting PP-wave String Field Theory
In this paper, we extend our previous study of causality and local
commutativity of string fields in the pp-wave lightcone string field theory to
include interaction. Contrary to the flat space case result of Lowe,
Polchinski, Susskind, Thorlacius and Uglum, we found that the pp-wave
interaction does not affect the local commutativity condition. Our results show
that the pp-wave lightcone string field theory is not continuously connected
with the flat space one. We also discuss the relation between the condition of
local commutativity and causality. While the two notions are closely related in
a point particle theory, their relation is less clear in string theory. We
suggest that string local commutativity may be relevant for an operational
defintion of causality using strings as probes.Comment: Latex, JHEP3.cls, 18 pages, no figures. v2: add comments about the
UV-IR mixing effect displayed in our result. version to appear in JHE
- …