Probing ultrafast spin-relaxation and precession dynamics in a cuprate Mott insulator with 7-fs optical pulses

A charge excitation in a two-dimensional Mott insulator is strongly coupled with the surrounding spins, which is observed as magnetic-polaron formations of doped carriers and a magnon sideband in the Mott-gap transition spectrum. However, the dynamics related to the spin sector are difficult to measure. Here, we show that pump-probe reflection spectroscopy with 7-fs laser pulses can detect the optically induced spin dynamics in Nd$_2$CuO$_4$, a cuprate Mott insulator. The bleaching signal at the Mott-gap transition is enhanced at $\sim$18 fs, which corresponds to the spin-relaxation time in magnetic-polaron formations and is characterized by the exchange interaction. More importantly, ultrafast coherent oscillations appear in the time evolutions of the reflectivity changes, and their frequencies (1400-2700 cm$^{-1}$) are equal to the probe energy measured from the Mott-gap transition peak. These oscillations originate from interferences between charge excitations with two magnons and provide direct evidence for charge-spin coupling.Comment: 20 pages including 4 figures (Supplementary materials: 11 pages including 4 figures

Large-scale STI services in Avahan improve utilization and treatment seeking behaviour amongst high-risk groups in India: an analysis of clinical records from six states

<p>Abstract</p> <p>Background</p> <p>Avahan, the India AIDS Initiative, implemented a large HIV prevention programme across six high HIV prevalence states amongst high risk groups consisting of female sex workers, high risk men who have sex with men, transgenders and injecting drug users in India. Utilization of the clinical services, health seeking behaviour and trends in syndromic diagnosis of sexually transmitted infections amongst these populations were measured using the individual tracking data.</p> <p>Methods</p> <p>The Avahan clinical monitoring system included individual tracking data pertaining to clinical services amongst high risk groups. All clinic visits were recorded in the routine clinical monitoring system using unique identification numbers at the NGO-level. Visits by individual clinic attendees were tracked from January 2005 to December 2009. An analysis examining the limited variables over time, stratified by risk group, was performed.</p> <p>Results</p> <p>A total of 431,434 individuals including 331,533 female sex workers, 10,280 injecting drug users, 82,293 men who have sex with men, and 7,328 transgenders visited the clinics with a total of 2,700,192 visits. Individuals made an average of 6.2 visits to the clinics during the study period. The number of visits per person increased annually from 1.2 in 2005 to 8.3 in 2009. The proportion of attendees visiting clinics more than four times a year increased from 4% in 2005 to 26% in 2009 (p<0.001). The proportion of STI syndromes diagnosed amongst female sex workers decreased from 39% in 2005 to 11% in 2009 (p<0.001) while the proportion of STI syndromes diagnosed amongst high risk men who have sex with men decreased from 12% to 3 % (p<0.001). The proportion of attendees seeking regular STI check-ups increased from 12% to 48% (p<0.001). The proportion of high risk groups accessing clinics within two days of onset of STI-related symptoms and acceptability of speculum and proctoscope examination increased significantly during the programme implementation period.</p> <p>Conclusions</p> <p>The programme demonstrated that acceptable and accessible services with marginalised and often difficult–to-reach populations can be brought to a very large scale using standardized approaches. Utilization of these services can dramatically improve health seeking behaviour and reduce STI prevalence.</p

Exploring the mechanism of tryptophan 2,3-dioxygenase

The haem proteins TDO (tryptophan 2,3-dioxygenase) and IDO (indoleamine 2,3-dioxygenase) are specific and powerful oxidation catalysts that insert one molecule of dioxygen into L-tryptophan in the first and rate-limiting step in the kynurenine pathway. Recent crystallographic and biochemical analyses of TDO and IDO have greatly aided our understanding of the mechanisms employed by these enzymes in the binding and activation of dioxygen and tryptophan. In the present paper, we briefly discuss the function, structure and possible catalytic mechanism of these enzymes

Changes in Antipsychotic Medication in Clients of Assertive Community Treatment in Japan: A One-Year Follow Up

The purpose of the present one-year follow-up study was to describe and investigate the change in the amount of antipsychotic drugs prescribed for ACT (assertive community treatment) clients in Japan. Subjects were 52 clients of ACT from January 2009 to December 2009. Prescription data were collected each month from the time the clients entered into ACT. The results of a Wilcoxon signed-rank test show that the dosage of antipsychotics significantly decreased from 1,131.3 mg to 731.3 mg over the course of the 12 months (Z = -2.505, p = 0.012)

African Communitarianism and Difference

There has been the recurrent suspicion that community, harmony, cohesion, and similar relational goods as understood in the African ethical tradition threaten to occlude difference. Often, it has been Western defenders of liberty who have raised the concern that these characteristically sub-Saharan values fail to account adequately for individuality, although some contemporary African thinkers have expressed the same concern. In this chapter, I provide a certain understanding of the sub-Saharan value of communal relationship and demonstrate that it entails a substantial allowance for difference. I aim to show that African thinkers need not appeal to, say, characteristically Euro-American values of authenticity or autonomy to make sense of why individuals should not be pressured to conform to a group’s norms regarding sex and gender. A key illustration involves homosexuality

The Mechanism of Substrate Inhibition in Human Indoleamine 2,3-Dioxygenase

Indoleamine 2,3-dioxygenase catalyzes the O(2)-dependent oxidation of L-tryptophan (L-Trp) to N-formylkynurenine (NFK) as part of the kynurenine pathway. Inhibition of enzyme activity at high L-Trp concentrations was first noted more than 30 years ago, but the mechanism of inhibition has not been established. Using a combination of kinetic and reduction potential measurements, we present evidence showing that inhibition of enzyme activity in human indoleamine 2,3-dioxygenase (hIDO) and a number of site-directed variants during turnover with L-tryptophan (L-Trp) can be accounted for by the sequential, ordered binding of O(2) and L-Trp. Analysis of the data shows that at low concentrations of L-Trp, O(2) binds first followed by the binding of L-Trp; at higher concentrations of L-Trp, the order of binding is reversed. In addition, we show that the heme reduction potential (E(m)(0)) has a regulatory role in controlling the overall rate of catalysis (and hence the extent of inhibition) because there is a quantifiable correlation between E(m)(0) (that increases in the presence of L-Trp) and the rate constant for O(2) binding. This means that the initial formation of ferric superoxide (Fe(3+)-O(2)(•-)) from Fe(2+)-O(2) becomes thermodynamically less favorable as substrate binds, and we propose that it is the slowing down of this oxidation step at higher concentrations of substrate that is the origin of the inhibition. In contrast, we show that regeneration of the ferrous enzyme (and formation of NFK) in the final step of the mechanism, which formally requires reduction of the heme, is facilitated by the higher reduction potential in the substrate-bound enzyme and the two constants (k(cat) and E(m)(0)) are shown also to be correlated. Thus, the overall catalytic activity is balanced between the equal and opposite dependencies of the initial and final steps of the mechanism on the heme reduction potential. This tuning of the reduction potential provides a simple mechanism for regulation of the reactivity, which may be used more widely across this family of enzymes