Stimulated Raman Adiabatic Passage via bright state in Lambda medium of unequal oscillator strengths

We consider the population transfer process in a Lambda-type atomic medium of unequal oscillator strengths by stimulated Raman adiabatic passage via bright-state (b-STIRAP) taking into account propagation effects. Using both analytic and numerical methods we show that the population transfer efficiency is sensitive to the ratio q_p/q_s of the transition oscillator strengths. We find that the case q_p>q_s is more detrimental for population transfer process as compared to the case where $q_p \leq q_s$. For this case it is possible to increase medium dimensions while permitting efficient population transfer. A criterion determining the interaction adiabaticity in the course of propagation process is found. We also show that the mixing parameter characterizing the population transfer propagates superluminally

Influence of positional correlations on the propagation of waves in a complex medium with polydisperse resonant scatterers

We present experimental results on a model system for studying wave propagation in a complex medium exhibiting low frequency resonances. These experiments enable us to investigate a fundamental question that is relevant for many materials, such as metamaterials, where low-frequency scattering resonances strongly influence the effective medium properties. This question concerns the effect of correlations in the positions of the scatterers on the coupling between their resonances, and hence on wave transport through the medium. To examine this question experimentally, we measure the effective medium wave number of acoustic waves in a sample made of bubbles embedded in an elastic matrix over a frequency range that includes the resonance frequency of the bubbles. The effective medium is highly dispersive, showing peaks in the attenuation and the phase velocity as functions of the frequency, which cannot be accurately described using the Independent Scattering Approximation (ISA). This discrepancy may be explained by the effects of the positional correlations of the scatterers, which we show to be dependent on the size of the scatterers. We propose a self-consistent approach for taking this "polydisperse correlation" into account and show that our model better describes the experimental results than the ISA

Two minor determinants of myelin basic protein induce experimental allergic encephalomyelitis in SJL/J mice

Experimental allergic encephalomyelitis (EAE)' is an autoimmune inflammatory demyelinating disease in the central nervous system (CNS) of animals immunized with myelin basic protein (MBP). The disease is directly mediated by Thelper cells that recognize MBP in the context ofclass II antigens of the MHC (1-3). In nude mice, a single clone of adoptively transferred MBP-reactive T helper cells can cause EAE (4), suggesting that these are the only T cells required for disease induction. As a prototypic model of T helper cell-mediated autoimmune disease, observations in EAE could likely be applicable to other T helper cell-mediated diseases such as murine lupus (5), thyroiditis (6), collagen arthritis (7), and adjuvant arthritis (8), as well as human autoimmune diseases. The MBP epitope is determined in part by the MHC. Using proteolytic peptide fragments of MBP, SJL/J (H-2s) and BIO.T(6R) (H-2q) mice were found to develop EAE to the COOH-terminal peptide of MBP, whereas PL/J (H-2u) and A/J (H-2k) mice developed EAE to the NH2-terminal peptide of MBP (9). Recently, by using synthetic peptides that overcome the difficulties of obtaining pure uncontaminated proteolytic peptides, a single T cell encephalitogenic epitope for PL/J mice has been identified . This epitope consists of the first nine NH2-terminal amino acid residues of MBP which must be acetylated at the a amino group to induce disease (10). Similar fine mapping of the encephalitogenic T cell epitope(s) for SJL/J mice has not been done, in part because of the large size of the COOH-terminal peptic fragment of MBP (residues 89-169 of rat MBP, reference 9). MouseMBP consists offour major forms due to differential RNA splicing of exons II and VI (11), resulting in molecular masses of 21, 18.5, 17.5, and 14 kD, in the relative amounts of 1 :10:3.5:35 . Since EAE can also be induced with the small form of rat MBP (14 kD), which has exons II and VI of the MBP gene deleted (12), the COOH-terminal encephalitogenic determinant for SJL/J mice must be present within a segment ofonly 42 amino acid residues . Consistent withthis notion is the observation that this peptide sequence is identical among the MBPs of several mammalian species, including mouse, rat, bovine, guinea pig, and porcine, all of which can induce EAE in SJL/mice (13, 14). To identify the SJL/J encephalitogenic T cell epitope(s), overlapping peptides to the COOH-terminal region ofthe small form of mouse MBP were synthesized. Two overlapping peptides encompassing an 18-amino acid region were found to elicit EAE in SJL/J mice. The finding of a single peptide region of MBP that is responsible for encephalitogenic T cell epitopes in SJL/J mice is analogous to that of the PL/J mice and has implications for the development of specific therapy for T cell-mediated autoimmune diseases

Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOx barriers

Perpendicular magnetic tunnel junctions with GdOX tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here we investigate the quality of the GdOX barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlOX and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence including sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier.Comment: 14 pages, 4 figure

Solar rotation rate and its gradients during cycle 23

Available helioseismic data now span almost the entire solar activity cycle 23 making it possible to study solar-cycle related changes of the solar rotation rate in detail. In this paper we study how the solar rotation rate, in particular, the zonal flows change with time. In addition to the zonal flows that show a well known pattern in the solar convection zone, we also study changes in the radial and latitudinal gradients of the rotation rate, particularly in the shear layer that is present in the immediate sub-surface layers of the Sun. In the case of the zonal-flow pattern, we find that the band indicating fast rotating region close to the equator seems to have bifurcated around 2005. Our investigation of the rotation-rate gradients show that the relative variation in the rotation-rate gradients is about 20% or more of their average values, which is much larger than the relative variation in the rotation rate itself. These results can be used to test predictions of various solar dynamo models.Comment: To appear in ApJ. Fig 5 has been corrected in this versio

A late Pleistocene long pollen record from Lake Urmia, NW Iran

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the upper last glacial sediments. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and upper part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences

Thermal Ground Testing of Concorde and Veras or Improvement in French Test Methods and Facilities

The more numerous the requirements are in aerospace vehicle operations, the more the ground test facility have to improve both the nature and the quality of the equipment as well as the volume and the size of the sites, for the importance of ground testing cannot be over emphasized. As an example, two ground test programs are reviewed in this presentation, namely CONCORDE and VERAS. Special emphasis is given to the facility implementations due respectively to the static and fatigue test of CONCORDE in heat environment and to the dynamic test of VERAS in high level and transient temperature conditions

Formalizing Size-Optimal Sorting Networks: Extracting a Certified Proof Checker

Since the proof of the four color theorem in 1976, computer-generated proofs have become a reality in mathematics and computer science. During the last decade, we have seen formal proofs using verified proof assistants being used to verify the validity of such proofs. In this paper, we describe a formalized theory of size-optimal sorting networks. From this formalization we extract a certified checker that successfully verifies computer-generated proofs of optimality on up to 8 inputs. The checker relies on an untrusted oracle to shortcut the search for witnesses on more than 1.6 million NP-complete subproblems.Comment: IMADA-preprint-c

Temporal variations of solar rotation rate at high latitudes

Frequency splitting coefficients from Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) observations covering the period 1995--2001 are used to study temporal variations in the solar rotation rate at high latitudes. The torsional oscillation pattern in the Sun is known to penetrate to a depth of about $0.1R_\odot$ with alternate bands of faster and slower rotating plasma. At lower latitudes the bands move towards equator with time. At higher latitudes, however, the bands appear to move towards the poles. This is similar to the observed pole-ward movement of large scale magnetic fields at high latitudes. This also supports theoretical results of pole-ward moving bands at high latitudes in some mean field dynamo models. The polar rotation rate is found to decrease between 1995 and 1999 after which it has started increasing.Comment: To appear in ApJ Letter

The non-enzymatic formation of nitric oxide from soil and clay systems

Prevailing concepts relating to the non-enzymatic gaseous loss of nitrite from soil are thought to be inadequate as regards to the mechanisms involved. The conventional explanation for nitric oxide formation i.e., the acid decomposition of nitrite, is held to be insufficient in substrates of only mild or slight acidity. A criticism is presented wherein it is maintained that certain past practices in methodology have created rather than eliminated confusion. Positive suggestions are proposed which may help to eliminate confusion in future experiments. Evidence was obtained from soil and clay systems which attest to a mechanism of loss whereby nitrite may react with certain metals to yield nitric oxide as a primary gaseous product. A conventional half-cell reaction is presented wherein a transition-like metal is oxidized and nitrite is reduced to nitric oxide with the formation of water. It is implied that hydrogen ions may be necessary--acid conditions favor the reduced state of the metals which is a more active state with respect to the formation of nitric oxide--for such reactions, but that they are not sufficient in substrates of only mild acidity. An apparent corollary to this study is that the very conditions which favor classical denitrification from nitrate also favor metal-nitrite reactions. Under such conditions both nitrate and the metals involved would be expected to undergo reduction resulting in an increased possibility for nitric oxide formation. This possibility places in question the status of nitric oxide as a direct biochemical intermediate in the microbial formation of nitrogen gas. It is suggested that a mechanism involving transition -like metals may account for significant losses of mineral nitrogen from field soils capable of accumulating nitrite under conditions of moderate or slight acidity