Propagation of a few-cycle laser pulse in a V-type three-level system

Propagation of a few-cycle laser pulse in a V-type three-level system (fine structure levels of rubidium) is investigated numerically. The full three-level Maxwell-Bloch equations without the rotating wave approximation and the standing slowly varying envelope approximation are solved by using a finite-difference time-domain method. It is shown that, when the usual unequal oscillator strengths are considered, self-induced transparency cannot be recovered and higher spectral components can be produced even for small-area pulses. (c) 2005 Pleiades Publishing, Inc.

The evolution of YidC/Oxa/Alb3 family in the three domains of life: a phylogenomic analysis

Background: YidC/Oxa/Alb3 family includes a group of conserved translocases that are essential for protein insertion into inner membranes of bacteria and mitochondria, and thylakoid membranes of chloroplasts. Because mitochondria and chloroplasts are of b

Effects of Lorentz local field correction on propagation properties of few-cycle pulse in dense Λ-type atomic medium

By solving numerically the full Maxwell-Bloch equations without the slowly varying envelope approximation and the rotating-wave approximation, we investigate the effects of Lorentz local field correction (LFC) on the propagation properties of few-cycle laser pulse in a dense A-type three-level atomic medium. We find that: when the area of the input pulse is larger, split of pulse occurs and the number of the sub-pulses with LFC is larger than that without LFC; at the same distance, the time interval between the first sub-pulse and the second sub-pulse in the case without LFC is longer than that with LFC, the time of pulse appearing in the case without LFC is later than that in the case with LFC, and the two phenomena are more obvious with propagation distance increasing; time evolution rules of the populations of levels vertical bar 1 >, vertical bar 2 > and vertical bar 3 > in the two cases with and without LFC are much different. When the area of the input pulse is smaller, effects of LFC on time evolutions of the pulse and populations are remarkably smaller than those in the case of larger area pulse. (c) 2008 Elsevier B.V. All rights reserved.

Phase control of gain and dispersion in an open V-type system

The control role of the relative phase between the probe and driving fields on gain, dispersion and populations in an open V-type three-level system with spontaneously generated coherence is studied. The result shows that by adjusting the value of the relative phase, the transformation between lasing with inversion and lasing without inversion (LWI) can be realized and high dispersion (refractive index) without absorption can be obtained. The shape and value range of the dispersion curve are similar to those of the gain curve, and this similarity is closely related to the relative phase. The effects of the atomic exit and injection rates and the incoherent pump rate on the control role of the relative phase are also analysed. It is found easier to get LWI by adjusting the value of the relative phase using the open system rather than the closed system, and using an incoherent pump rather than without using the incoherent pump. Moreover the open system can give a larger LWI gain than the closed system.

Domain structure of hard magnetic NdAlFeCo bulk metallic glass

Magnetic domain structure of hard magnetic Nd60Al10Fe20Co10 bulk metallic glass (BMG) has been studied by using magnetic force microscopy. In the magnetic force images it is shown that the exchange interaction type magnetic domains with a period of about 360 nm do exist in the BMG, which is believed to be associated with the appearance of hard-magnetic properties in this system. As the scale of the magnetic domain is much larger than the size of the short-range ordered atomic clusters existing in the BMG, it is believed that the large areas of magnetic contrast are actually a collection of a group of clusters aligned in parallel by strong exchange coupling interaction. After fully crystallization, the BMG exhibits paramagnetism. No obvious magnetic contrast is observed in the magnetic force images of fully crystallized samples, except for a small quantity of ferromagnetic crystalline phase with low coercivity and an average size of 900 nm.

Domain structure of a Nd60Al10Fe20Co10 bulk metallic glass

Magnetic domain structure of Nd60Al10Fe20Co10 bulk metallic glass (BMG) has been studied by using magnetic-force microscopy. In the magnetic-force images it is shown that the exchange-interaction-type magnetic domains with a period of about 360 nm do exist in the BMG, which is believed to be associated with the appearance of hard-magnetic properties in this system. The existence of the large-scale domains demonstrates that the magnetic moments of a great deal of short-scale ordered atomic clusters in the BMG have been aligned by exchange coupling. Annealing at 715 K leads to partial crystallization of the BMG. However, the exchange coupling is stronger in the annealed sample, which is considered to arise from the increase of transition-metal concentration in the amorphous phase due to the precipitation of Nd crystalline phase.

Investigation of transient process and steady output of lasing without inversion

The transient evolution processes and steady outputs of continuous wave lasing without inversion (LWI) and self-pulsing LWI in a resonant open V type three-level system are studied. It was found that the two kinds of LWI have some obvious differences not only from the steady outputs but also from the transient evolution processes. The effects of the unsaturated gain coefficient, cavity loss coefficient, ratio of the atomic injection rates and atomic exit rate on the transient evolution processes and steady outputs are discussed.

Controllable Kerr nonlinearity with perfect transparency in the existence of spontaneously generated coherence

We investigate the Kerr nonlinearity of a V-type three-level atomic system where the upper two states decay outside to another state and hence spontaneous generated coherence may exist. It is shown that dark state and hence perfect transparency present under certain conditions. Meanwhile, the Kerr nonlinearity can be controlled by manipulation of the decay rates and the splitting of the two excited states. Therefore, enhanced Kerr nonlinearity without absorption can be obtained under proper parameters.

合成孔径激光成像雷达(Ⅰ):离焦和相位偏置望远镜接收天线

把合成孔径激光成像雷达的目标衍射区分为三个区域,提出采用离焦或者附加空间相位调制板的光学接收望远镜补偿回波像差。当目标处于菲涅耳衍射区时可采用离焦或偏置望远镜补偿回波二次项离焦像差并产生用于孔径合成的二次项相位历程;目标处于夫琅和费衍射区时可以采用离焦或偏置望远镜补偿回波二次项离焦像差但不产生相位历程;目标处于瑞利-索末菲衍射区域时不可能补偿回波高阶像差。

Adaptive evolution of a duplicated pancreatic ribonuclease gene in a leaf-eating monkey

Although the complete genome sequences of over 50 representative species have revealed the many duplicated genes in all three domains of life(1-4), the roles of gene duplication in organismal adaptation and biodiversity are poorly understood. In addition,

Analysis of the intein's evolution

Inteins are internal segment peptides which can self-splicing at the protein level. Although inteins are found in all three domains of life, they are not evenly distributed among species and proteins. So the evolution of intein have been capturing much at

Identification of triosephosphate isomerase (TIM) genes from Microcystis (Cyanobacteria : Chroococcales) and theoretical analyses of the potential of cyanobacterial TIM as a target for designing specific inhibitors

The genes encoding triosephosphate isomerase (TIM) in three species of Microcystis (M. aeruginosa, M. viridis and M. wesenbergii) were investigated. Reverse transcriptase-polymerase chain reaction indicated that they were transcribed in the cells. Analyses showed that their DNA and deduced amino acid sequences were highly conserved between all the three species, only a single nonsynonymous substitution was seen at position 31, from an Asp in M. aeruginosa and M. viridis to Glu in M. wesenbergii. Sequence alignment of these with 12 other known cyanobacterial TIM sequences showed that all the cyanobacterial TIMs had a very high level of amino acid identity (over 50% between each two). Comparison of the cyanobacterial TIMs with other reported TIMs (from diverse lineages of the three Domains) showed that they possessed common active-site residues and sequence motifs. All cyanobacterial TIMs have two common cysteine residues (Cys127 and Cys176), and the Cys176 is almost cyanobacteria-specific with only one exception in Streptomyces coelicolor. Both secondary structure alignment and comparative modelling of Synechocystis sp. TIM showed that Cys176 was located at the hinge region of the flexible loop-6 and might therefore be critical to the movement of TIM's loop-6, which is important to the function of the enzyme. Thus, the cyanobacterial TIM-specific Cys176 may be a potential site for the discovery of suitable drugs against cyanobacteria, and such drugs may have utility in controlling water blooms due to cyanobacteria.

Gene structure of an antimicrobial peptide from mandarin fish, Siniperca chuatsi (Basilewsky), suggests that moronecidins and pleurocidins belong in one family: the piscidins

The gene of piscidin, an antimicrobial peptide, has been cloned from the mandarin fish, Siniperca chuatsi. From the first transcription initiation site, the mandarin fish piscidin gene extends 1693 nucleotides to the end of the 3' untranslated region and contains four exons and three introns. A predicted 79-residue prepropeptide consists of three domains: a signal peptide (22 aa), a mature peptide (22 aa) and a C-terminal prodomain (35 aa). The shortage of XQQ motif in the prodomain of mandarin fish piscidin and the similar gene structure between moronecidins (piscidins) and pleurocidins may indicate that they are derived from the same ancestor gene. We thus suggest that piscidin should be used as a terminology for these antimicrobial peptides in the future. The mandarin fish piscidin mRNA was abundant in intestine, spleen, pronephros and kidney analysed by real-time polymerase chain reaction. After stimulation with lipopoly saccharides (LPS), a marked increase in transcripts was observed in most tissues, indicating that piscidin is not only a constitutively expressed molecule, but also has an increased response to bacterial infection. The synthetic, amidated mandarin fish piscidin exhibited different antimicrobial activity against different fish bacterial pathogens, especially against species of Aeromonas, which may to certain extent reflect the pathogenicity of these bacteria.

Identification of a novel cathelicidin gene in the rainbow trout, Oncorhynchus mykiss

We report the cloning of a novel antimicrobial peptide gene, termed rtCATH_1, found in the rainbow trout, Oncorhynchus mykiss. The predicted 216-residue rtCATH_1 prepropeptide consists of three domains: a 22-residue signal peptide, a 128-residue cathelin-like region containing two identifiable cathelicidin family signatures, and a predicted 66-residue C-terminal cationic antimicrobial peptide. This predicted mature peptide was unique in possessing features of different known (mammalian) cathelicidin subgroups, such as the cysteine-bridged family and the specific amino-acid-rich family. The rtCATH_1 gene comprises four exons, as seen in all known mammalian cathelicidin genes, and several transcription factor binding sites known to be of relevance to host defenses were identified in the 5' flanking region. By Northern blot analysis, the expression of rtCATH_1 was detected in gill, head kidney, and spleen of bacterially challenged fish. Primary cultures of head kidney leukocytes from rainbow trout stimulated with lipopolysaccharide or poly(I (.) C) also expressed riCATH_1. A 36-residue peptide corresponding to the core part of the fish cathelicidin was chemically synthesized and shown to exhibit potent antimicrobial activity and a low hemolytic effect. Thus, rtCATH_1 represents a novel antimicrobial peptide gene belonging to the cathelicidin family and may play an important role in the innate immunity of rainbow trout.

A novel C-type lectin (Cflec-3) from Chlamys farreri with three carbohydrate-recognition domains

C-type lectins are a superfamily of carbohydrate-recognition proteins which play crucial roles in the innate immunity. In this study, the gene of a C-type lectin with multiple carbohydrate-recognition domains (CRDs) from scallop Chlamys farreri (designated as Cflec-3) was cloned by rapid amplification of cDNA ends (RACE) approach based on expression sequence tag (EST) analysis. The full-length cDNA of Cflec-3 was of 2256 bp. The open reading frame encoded a polypeptide of 516 amino acids, including a signal sequence and three CRDs. The deduced amino acid sequence of Cflec-3 showed high similarity to members of C-type lectin superfamily. By fluorescent quantitative real-time PCR, the Cflec-3 mRNA was mainly detected in hepatopancreas, adductor, mantle, and marginally in gill, gonad and hemocytes of healthy scallops. After scallops were challenged by Listonella anguillarum, the mRNA level of Cflec-3 in hemocytes was up-regulated and was significantly higher than that of blank at 8 h and 12 h post-challenge. The function of Cflec-3 was investigated by recombination and expression of the cDNA fragment encoding its mature peptide in Escherichia coli BL21 (DE3)-pLysS. The recombined Cflec-3 (rCflec-3) agglutinated Gram-negative bacteria Pseudomonas stutzeri. The agglutinating activity was calcium-dependent and could be inhibited by D-mannose. These results collectively suggested that Cflec-3 was involved in the immune response against microbe infection and contributed to nonself-recognition and clearance of bacterial pathogens in scallop. (C) 2009 Elsevier Ltd. All rights reserved.