6,561 research outputs found
Bichromatically driven double well: parametric perspective of the strong-field control landscape reveals the influence of chaotic states
The aim of this work is to understand the influence of chaotic states in
control problems involving strong fields. Towards this end, we numerically
construct and study the strong field control landscape of a bichromatically
driven double well. A novel measure based on correlating the overlap
intensities between Floquet states and an initial phase space coherent state
with the parametric motion of the quasienergies is used to construct and
interpret the landscape features. "Walls" of no control, robust under
variations of the relative phase between the fields, are seen on the control
landscape and associated with multilevel interactions involving chaotic Floquet
states.Comment: 9 pages and 6 figures. Rewritten and expanded version of
arXiv:0707.4547 [nlin.CD]. Accepted for publication in J. Chem. Phys. (2008
Local phase space control and interplay of classical and quantum effects in dissociation of a driven Morse oscillator
This work explores the possibility of controlling the dissociation of a
monochromatically driven one-dimensional Morse oscillator by recreating
barriers, in the form of invariant tori with irrational winding ratios, at
specific locations in the phase space. The control algorithm proposed by Huang
{\it et al.} (Phys. Rev. A {\bf 74}, 053408 (2006)) is used to obtain an
analytic expression for the control field. We show that the control term,
approximated as an additional weaker field, is efficient in recreating the
desired tori and suppresses the classical as well as the quantum dissociation.
However, in the case when the field frequency is tuned close to a two-photon
resonance the local barriers are not effective in suppressing the dissociation.
We establish that in the on-resonant case quantum dissociation primarily occurs
via resonance-assisted tunneling and controlling the quantum dynamics requires
a local perturbation of the specific nonlinear resonance in the underlying
phase space.Comment: 12 pages, 6 figures (reduced quality), submitted to Phys. Rev.
A space-time channel estimator and single-user receiver for code-reuse DS-CDMA systems
Published versio
Can We Detect the Anisotropic Shapes of Quasar HII Regions During Reionization Through The Small-Scale Redshifted 21cm Power Spectrum?
Light travel time delays distort the apparent shapes of HII regions
surrounding bright quasars during early stages of cosmic reionization.
Individual HII regions may remain undetectable in forthcoming redshifted 21 cm
experiments. However, the systematic deformation along the line of sight may be
detectable statistically, either by stacking tomographic 21cm images of quasars
identified, for example, by JWST, or as small-scale anisotropy in the
three-dimensional 21cm power spectrum. Here we consider the detectability of
this effect. The anisotropy is largest when HII regions are large and expand
rapidly, and we find that if bright quasars contributed to the early stages of
reionization, then they can produce significant anisotropy, on scales
comparable to the typical sizes of HII regions of the bright quasars (approx.
30 Mpc and below). The effect therefore cannot be ignored when analyzing future
21cm power spectra on small scales. If 10 percent of the volume of the IGM at
redshift z=10 is ionized by quasars with typical ionizing luminosity of S= 5 x
10^{56} photons/second, the distortions can enhance by more than 10 percent the
21cm power spectrum in the radial (redshift) direction, relative to the
transverse directions. The level of this anisotropy exceeds that due to
redshift-space distortion, and has the opposite sign. We show that on-going
experiments such as MWA should be able to detect this effect. A detection would
reveal the presence of bright quasars, and shed light on the ionizing yield and
age of the ionizing sources, and the distribution and small-scale clumping of
neutral intergalactic gas in their vicinity.Comment: Version accepted by ApJ, with new fiducial model and improved
discussio
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Emerging Evidence for MicroRNAs as Regulators of Cancer Stem Cells
Cancer stem cells are defined as a subpopulation of cells within a tumor that are capable of self-renewal and differentiation into the heterogeneous cell lineages that comprise the tumor. Many studies indicate that cancer stem cells may be responsible for treatment failure and relapse in cancer patients. The factors that regulate cancer stem cells are not well defined. MicroRNAs (miRNAs) are small non-coding RNAs that regulate translational repression and transcript degradation. miRNAs play a critical role in embryonic and inducible pluripotent stem cell regulation and emerging evidence supports their role in cancer stem cell evolution. To date, miRNAs have been shown to act either as tumor suppressor genes or oncogenes in driving critical gene expression pathways in cancer stem cells in a wide range of human malignancies, including hematopoietic and epithelial tumors and sarcomas. miRNAs involved in cancer stem cell regulation provide attractive, novel therapeutic targets for cancer treatment. This review attempts to summarize progress to date in defining the role of miRNAs in cancer stem cells
A Curious Truncation of N=4 Yang-Mills
The coupling constant dependence of correlation functions of BPS operators in
N=4 Yang-Mills can be expressed in terms of integrated correlation functions.
We approximate these integrated correlators by using a truncated OPE expansion.
This leads to differential equations for the coupling dependence. When applied
to a particular sixteen point correlator, the coupling dependence we find
agrees with the corresponding amplitude computed via the AdS/CFT
correspondence. We conjecture that this truncation becomes exact in the large N
and large 't Hooft coupling limit.Comment: 10 pages, LaTeX; additional comments, added reference
Enabling Context-Based Learning with KPortal Webspace Technology
Recognizing the importance of context-based learning and the general lack of technology applications in the design and development of the ideal and formal curricula, this paper describes an experimental system at a large public university. The authors describe the creation of a contextual environment for introducing concepts related to information security to undergraduate business students using the KPortal (Knowledge Portals) webspace technology that supports dynamic content gathered from various sources automatically. The KPortal webspace rated highly on the various attributes of effective contexts and the characteristics of technologies that enable context-based learning. The flexibility provided by the webspace permitted the authors to develop adaptable environments in which the students could connect well with rather abstract concepts. The overall intervention was designed to examine if a limited portion of the course could be supported by technology and next phases of the research will broaden its use to semester-length curriculum
Bony impressions on caput and neck of human femora in Indian Population.
Idiopathic osteoarthritis of the hip has been currently attributed by researchers to the repetitive microtrauma caused to the femoral neck by its impingement against the acetabular rim. This impingement occurs as a result of abnormal morphological traits like Allen’s fossa, Poirier’s Facet, and Posterior Cervical Imprint that appear on the proximal end of femur especially on the neck. Hence, this study was undertaken to investigate the incidence of these traits in the Indian population and to find a correlation between the occurrence of the trait and the side and sex of the bone. The study was conducted on 152 adult dried femora in the Department of Anatomy, Maulana Azad Medical College, New Delhi, India. The positive findings were photographed. The significance of the correlation was found out using Chi-square test. Allen’s Fossa was found to occur in 71.1% of the total bones assessed Poirier’s Facet in 31.6% and Posterior Cervical Imprint in 19.7%. Out of these, a significant side association was found for the Poirier’s Facet with a predominance of the left side. All the traits were found to be more in males with a significant sex variation for Poirier’s Facet. Each trait demonstrated a significant side and gender dimorphism
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