395 research outputs found
Nonlinear dynamics of a solid-state laser with injection
We analyze the dynamics of a solid-state laser driven by an injected
sinusoidal field. For this type of laser, the cavity round-trip time is much
shorter than its fluorescence time, yielding a dimensionless ratio of time
scales . Analytical criteria are derived for the existence,
stability, and bifurcations of phase-locked states. We find three distinct
unlocking mechanisms. First, if the dimensionless detuning and
injection strength are small in the sense that , unlocking occurs by a saddle-node infinite-period bifurcation.
This is the classic unlocking mechanism governed by the Adler equation: after
unlocking occurs, the phases of the drive and the laser drift apart
monotonically. The second mechanism occurs if the detuning and the drive
strength are large: . In this regime, unlocking
is caused instead by a supercritical Hopf bifurcation, leading first to phase
trapping and only then to phase drift as the drive is decreased. The third and
most interesting mechanism occurs in the distinguished intermediate regime . Here the system exhibits complicated, but
nonchaotic, behavior. Furthermore, as the drive decreases below the unlocking
threshold, numerical simulations predict a novel self-similar sequence of
bifurcations whose details are not yet understood.Comment: 29 pages in revtex + 8 figs in eps. To appear in Phys. Rev. E
(scheduled tentatively for the issue of 1 Oct 98
Retarded long-range potentials for the alkali-metal atoms and a perfectly conducting wall
The retarded long-range potentials for hydrogen and alkali-metal atoms in
their ground states and a perfectly conducting wall are calculated. The
potentials are given over a wide range of atom-wall distances and the validity
of the approximations used is established.Comment: RevTeX, epsf, 11 pages, 2 fig
Time-dependent calculation of ionization in Potassium at mid-infrared wavelengths
We study the dynamics of the Potassium atom in the mid-infrared, high
intensity, short laser pulse regime. We ascertain numerical convergence by
comparing the results obtained by the direct expansion of the time-dependent
Schroedinger equation onto B-Splines, to those obtained by the eigenbasis
expansion method. We present ionization curves in the 12-, 13-, and 14-photon
ionization range for Potassium. The ionization curve of a scaled system, namely
Hydrogen starting from the 2s, is compared to the 12-photon results. In the
13-photon regime, a dynamic resonance is found and analyzed in some detail. The
results for all wavelengths and intensities, including Hydrogen, display a
clear plateau in the peak-heights of the low energy part of the Above Threshold
Ionization (ATI) spectrum, which scales with the ponderomotive energy Up, and
extends to 2.8 +- 0.5 Up.Comment: 15 two-column pages with 15 figures, 3 tables. Accepted for
publication in Phys. Rev A. Improved figures, language and punctuation, and
made minor corrections. We also added a comparison to the ADK theor
Theory and applications of atomic and ionic polarizabilities
Atomic polarization phenomena impinge upon a number of areas and processes in
physics. The dielectric constant and refractive index of any gas are examples
of macroscopic properties that are largely determined by the dipole
polarizability. When it comes to microscopic phenomena, the existence of
alkaline-earth anions and the recently discovered ability of positrons to bind
to many atoms are predominantly due to the polarization interaction. An
imperfect knowledge of atomic polarizabilities is presently looming as the
largest source of uncertainty in the new generation of optical frequency
standards. Accurate polarizabilities for the group I and II atoms and ions of
the periodic table have recently become available by a variety of techniques.
These include refined many-body perturbation theory and coupled-cluster
calculations sometimes combined with precise experimental data for selected
transitions, microwave spectroscopy of Rydberg atoms and ions, refractive index
measurements in microwave cavities, ab initio calculations of atomic structures
using explicitly correlated wave functions, interferometry with atom beams, and
velocity changes of laser cooled atoms induced by an electric field. This
review examines existing theoretical methods of determining atomic and ionic
polarizabilities, and discusses their relevance to various applications with
particular emphasis on cold-atom physics and the metrology of atomic frequency
standards.Comment: Review paper, 44 page
Beyond the caveman: Rethinking masculinity in relation to men’s help-seeking
publication-status: Publishedtypes: ArticleStatistically, men make less use of health-care services than women. This has been
interpreted as the result of the ‘hegemonic’ masculine code in which ‘real’ men are
understood to be physically fit, uninterested in their health and self-reliant. However,
less attention has been paid to understanding how hegemonic masculinity intersects
with the wider western socio-cultural contexts of men’s help-seeking, particularly
the valorization of health as a form of social achievement. This article presents the
results of interviews with 14 higher socio-economic status (SES) men to uncover their
‘interpretive repertoires’ in relation to health and illness, help-seeking and masculinity.
Although many interviewees drew on the stereotype of the ‘Neanderthal Man’ who
avoids the doctors to explain help-seeking by men ‘in general’, they constructed their
own experiences of help-seeking in terms of being responsible, problem-solving and in
control. It is argued that the framing of help-seeking in terms of ‘taking action’ chimes
with an increasingly pro-active ‘expert patient’ approach within western health-care.
This conceptual reconstruction of the dominant masculine code in relation to helpseeking,
from ‘Neanderthal Man’ to ‘Action Man’, may lead to greater gender equality
in terms of accessing health-care. However, it has the potential to exacerbate social
inequalities between men from different SES groups
Development and Validation of the Behavioral Tendencies Questionnaire
At a fundamental level, taxonomy of behavior and behavioral tendencies can be described
in terms of approach, avoid, or equivocate (i.e., neither approach nor avoid). While there are
numerous theories of personality, temperament, and character, few seem to take advantage
of parsimonious taxonomy. The present study sought to implement this taxonomy by
creating a questionnaire based on a categorization of behavioral temperaments/tendencies
first identified in Buddhist accounts over fifteen hundred years ago. Items were developed
using historical and contemporary texts of the behavioral temperaments, described as
“Greedy/Faithful”, “Aversive/Discerning”, and “Deluded/Speculative”. To both maintain
this categorical typology and benefit from the advantageous properties of forced-choice
response format (e.g., reduction of response biases), binary pairwise preferences for items
were modeled using Latent Class Analysis (LCA). One sample (n1 = 394) was used to estimate
the item parameters, and the second sample (n2 = 504) was used to classify the participants
using the established parameters and cross-validate the classification against
multiple other measures. The cross-validated measure exhibited good nomothetic span
(construct-consistent relationships with related measures) that seemed to corroborate the
ideas present in the original Buddhist source documents. The final 13-block questionnaire
created from the best performing items (the Behavioral Tendencies Questionnaire or BTQ)
is a psychometrically valid questionnaire that is historically consistent, based in behavioral
tendencies, and promises practical and clinical utility particularly in settings that teach and
study meditation practices such as Mindfulness Based Stress Reduction (MBSR)
Lead optimization of a pyrazole sulfonamide series of trypanosoma brucei N -myristoyltransferase inhibitors:Identification and evaluation of CNS penetrant compounds as potential treatments for stage 2 human african trypanosomiasis
[Image: see text] Trypanosoma bruceiN-myristoyltransferase (TbNMT) is an attractive therapeutic target for the treatment of human African trypanosomiasis (HAT). From previous studies, we identified pyrazole sulfonamide, DDD85646 (1), a potent inhibitor of TbNMT. Although this compound represents an excellent lead, poor central nervous system (CNS) exposure restricts its use to the hemolymphatic form (stage 1) of the disease. With a clear clinical need for new drug treatments for HAT that address both the hemolymphatic and CNS stages of the disease, a chemistry campaign was initiated to address the shortfalls of this series. This paper describes modifications to the pyrazole sulfonamides which markedly improved blood–brain barrier permeability, achieved by reducing polar surface area and capping the sulfonamide. Moreover, replacing the core aromatic with a flexible linker significantly improved selectivity. This led to the discovery of DDD100097 (40) which demonstrated partial efficacy in a stage 2 (CNS) mouse model of HAT
Psychologists’ Authenticity: Implications for Work in Professional and Therapeutic Settings
Derek J. Burks, PhD, is a licensed psychologist and postdoctoral psychology fellow at the Pacific Northwest Mental Illness Research, Education, and Clinical Center (MIRECC), located within the Veterans Affairs Medical Center in Portland, Oregon. He obtained his PhD in counseling psychology from the University of Oklahoma. His current research focuses on health disparities, posttraumatic stress disorder among sexual-minority U.S. military veterans, and culturally appropriate mental health treatment for American Indians.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Trisubstituted Pyrimidines as Efficacious and Fast-acting Antimalarials
In this paper we describe the optimization of a phenotypic hit against Plasmodium falciparum, based on a trisubstituted pyrimidine scaffold. This led to compounds with good pharmacokinetics and oral activity in a P. berghei mouse model of malaria. The most promising compound (13) showed a reduction in parasitemia of 96% when dosed at 30 mg/kg orally once a day for 4 days in the P. berghei mouse model of malaria. It also demonstrated a rapid rate of clearance of the erythrocytic stage of P. falciparum in the SCID mouse model with an ED90 of 11.7 mg/kg when dosed orally. Unfortunately, the compound is a potent inhibitor of cytochrome P450 enzymes, probably due to a 4-pyridyl substituent. Nevertheless, this is a lead molecule with a potentially useful antimalarial profile, which could either be further optimized or be used for target hunting
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