Strong light fields coax intramolecular reactions on femtosecond time scales

Energetic H$_2^+$ ions are formed as a result of intra-molecular rearrangement during fragmentation of linear alcohols (methanol, ethanol, propanol, hexanol, and dodecanol) induced by intense optical fields produced by 100 fs long, infrared, laser pulses of peak intensity 8$\times10^{15}$ W cm$^{-2}$. Polarization dependent measurements show, counterintuitively, that rearrangement is induced by the strong optical field within a single laser pulse, and that it occurs before Coulomb explosion of the field-ionized multiply charged alcohols

Ionization and Coulomb explosion of Xenon clusters by intense, few-cycle laser pulses

Intense, ultrashort pulses of 800 nm laser light (12 fs, $\sim$4 optical cycles) of peak intensity 5$\times$10$^{14}$ W cm$^{-2}$ have been used to irradiate gas-phase Xe$_n$ clusters ($n$=500-25,000) so as to induce multiple ionization and subsequent Coulomb explosion. Energy distributions of exploding ions are measured in the few-cycle domain that does not allow sufficient time for the cluster to undergo Coulomb-driven expansion. This results in overall dynamics that appear to be significantly different to those in the many-cycle regime. One manifestation is that the maximum ion energies are measured to be much lower than those obtained when longer pulses of the same intensity are used. Ion yields are cluster-size independent but polarization dependent in that they are significantly larger when the polarization is perpendicular to the detection axis than along it. This unexpected behavior is qualitatively rationalized in terms of a spatially anisotropic shielding effect induced by the electronic charge cloud within the cluster

Extremal Correlators in the AdS/CFT Correspondence

The non-renormalization of the 3-point functions $tr X^{k_1} tr X^{k_2} tr X^{k_3}$ of chiral primary operators in N=4 super-Yang-Mills theory is one of the most striking facts to emerge from the AdS/CFT correspondence. A two-fold puzzle appears in the extremal case, e.g. k_1 = k_2 + k_3. First, the supergravity calculation involves analytic continuation in the k_i variables to define the product of a vanishing bulk coupling and an infinite integral over AdS. Second, extremal correlators are uniquely sensitive to mixing of the single-trace operators $tr X^k$ with protected multi-trace operators in the same representation of SU(4). We show that the calculation of extremal correlators from supergravity is subject to the same subtlety of regularization known for the 2-point functions, and we present a careful method which justifies the analytic continuation and shows that supergravity fields couple to single traces without admixture. We also study extremal n-point functions of chiral primary operators, and argue that Type IIB supergravity requires that their space-time form is a product of n-1 two-point functions (as in the free field approximation) multiplied by a non-renormalized coefficient. This non-renormalization property of extremal n-point functions is a new prediction of the AdS/CFT correspondence. As a byproduct of this work we obtain the cubic couplings $t \phi \phi$ and $s \phi \phi$ of fields in the dilaton and 5-sphere graviton towers of Type IIB supergravity on $AdS_5 \times S^5$.Comment: 26 pages, LateX, no figure

The information paradox: conflicts and resolutions

Many relativists have been long convinced that black hole evaporation leads to information loss or remnants. String theorists have however not been too worried about the issue, largely due to a belief that the Hawking argument for information loss is flawed in its details. A recently derived inequality shows that the Hawking argument for black holes with horizon can in fact be made rigorous. What happens instead is that in string theory black hole microstates have no horizons. Thus the evolution of radiation quanta with E ~ kT is modified by order unity at the horizon, and we resolve the information paradox. We discuss how it is still possible for E >> kT objects to see an approximate black hole like geometry. We also note some possible implications of this physics for the early Universe.Comment: 26 pages, 8 figures, Latex; (Expanded version of) proceedings for Lepton-Photon 201

Extracting surface rotation periods of solar-like Kepler targets

We use various method to extract surface rotation periods of Kepler targets exhibiting solar-like oscillations and compare their results.Comment: Proceedings of the CoRoT3-KASC7 Conference. 2 pages, 1 figur

Intense 2-cycle laser pulses induce time-dependent bond-hardening in a polyatomic molecule

A time-dependent bond-hardening process is discovered in a polyatomic molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm light. In conventional mass spectrometry, symmetrical molecules like TMS do not exhibit a prominent molecular ion (TMS$^+$) as unimolecular dissociation into [Si(CH$_3$)$_3]^+$ proceeds very fast. Under strong field and few-cycle conditions, this dissociation channel is defeated by time-dependent bond-hardening: a field-induced potential well is created in the TMS$^+$ potential energy curve that effectively traps a wavepacket. The time-dependence of this bond hardening process is verified using longer-duration ($\geq$ 100 fs) pulses; the relatively "slower" fall-off of optical field in such pulses allows the initially trapped wavepacket to leak out, thereby rendering TMS$^+$ unstable once again. Our results are significant as they demonstrate (i) optical generation of polyatomic ions that are normally inaccessible and (ii) optical control of dynamics in strong fields, with distinct advantages over weak-field control scenarios that demand a narrow bandwidth appropriate for a specified transition.Comment: To appear in Phys. Rev. Let

Adipokines and body fat composition in South Asians: results of the Metabolic Syndrome and Atherosclerosis in South Asians Living in America (MASALA) study.

ObjectiveTo investigate whether leptin and adiponectin are associated with body fat composition in a South Asian population independent of metabolic variables.DesignCross-sectional study.Subjects150 South Asian men and women, between the ages of 45-79 years, in the San Francisco Bay Area without pre-existing clinical cardiovascular disease.MeasurementsBlood samples were obtained to measure glucose metabolism variables, lipid profiles and adipokines. Total body fat was determined using dual-energy X-ray absorptiometry. Abdominal computed tomography was used to measure subcutaneous, visceral and hepatic fat.ResultsAverage body mass index (BMI) was overweight at 26.1±4.6 kg m(-2) and did not differ by sex. However, women had significantly more total body fat (P<0.001) and subcutaneous fat (P<0.001) than men, whereas men had significantly more visceral fat (P<0.001) and hepatic fat (P=0.04) than women. Women had significantly higher levels of adiponectin (P<0.01) and leptin (P<0.01). In sex-stratified analyses, leptin was strongly associated with all-body composition measures in women (P<0.05) as well as in men (P<0.05 except for hepatic fat), whereas there was an insignificant trend towards an inverse association between adiponectin and body composition in both women and men, which was significant in combined bivariate analyses. In multivariate analyses, leptin was strongly associated with all measures of adiposity, including BMI (P<0.001), total body fat (P<0.001), visceral fat (P<0.001) and hepatic fat (P=0.01). However, adiponectin's inverse association with adiposity was significantly attenuated by high-density lipoprotein (HDL), triglycerides and insulin resistance. The association between adipokines and diabetes was markedly attenuated after adjusting for body composition.ConclusionDespite only modestly elevated BMI, South Asians have elevated levels of total and regional adiposity. Leptin is strongly associated with adiposity, whereas adiponectin's association with adiposity is attenuated by metabolic variables in South Asians. Adipokines in association with adiposity have an important role in the development of diabetes