ABSTRACT
Semiconductor microcavities are frequently studied in the context of semiconductor lasers and in application-oriented fundamental research on topics such as linear and nonlinear polariton systems, polariton lasers, polariton pattern formation, and polaritonic Bose-Einstein condensates. A commonly used approach to describe theoretical properties includes a phenomenological single-mode equation that complements the equation for the nonlinear optical response (interband polarization) of the semiconductor. Here, we show how to replace the single-mode equation by a fully predictive transfer function method that, in contrast to the single-mode equation, accounts for propagation, retardation, and pulse-filtering effects of the incident light field traversing the distributed Bragg reflector (DBR) mirrors, without substantially increasing the numerical complexity of the solution. As examples, we use cavities containing GaAs quantum wells and transition-metal dichalcogenides (TMDs).
ABSTRACT
Applications of the orbital angular momentum (OAM) of light range from the next generation of optical communication systems to optical imaging and optical manipulation of particles. Here we propose a micron-sized semiconductor source that emits light with predefined OAM pairs. This source is based on a polaritonic quantum fluid. We show how in this system modulational instabilities can be controlled and harnessed for the spontaneous formation of OAM pairs not present in the pump laser source. Once created, the OAM states exhibit exotic flow patterns in the quantum fluid, characterized by generation-annihilation pairs. These can only occur in open systems, not in equilibrium condensates, in contrast to well-established vortex-antivortex pairs.
ABSTRACT
We present a quantum dynamical study of exciton transfer across a torsional defect that locally breaks the pi-conjugation in an oligo-(p-phenylene vinylene) (OPV) fragment. A site-based vibronic coupling Hamiltonian is used which is formulated in a comparative fashion (i) for a Frenkel exciton basis, assuming localized electron-hole pairs whose superposition yields a delocalized exciton, and (ii) more accurately, for a Merrifield type exciton basis including spatially separated electron-hole pairs. Starting from a partially delocalized ("spectroscopic unit") initial condition, the observed transfer dynamics is found to involve two characteristic time scales: (i) a very rapid, coherent transient on a 10-100 femtosecond scale, largely determined by Rabi type oscillations modulated by bond-length-alternation modes, and (ii) a slower time scale involving the planarization of the torsional coordinates that determines the onset of a quasi-stationary exciton-polaron state, and in the process leads to a "healing" of the torsional defect within - 500 femtoseconds. The dynamics obtained from the full electron-hole basis vs. Frenkel basis are in good agreement. In the full electron-hole dynamics, the transients are found to involve a rapid expansion and subsequent contraction of the electron-hole coherence size. Quantum dynamical simulations for a minimal six-site model involving 36 states and 22 vibrational modes, were carried out using the multiconfiguration time dependent Hartree (MCTDH) method.
ABSTRACT
Epithelial renewal in skin is achieved by the constant turnover and differentiation of keratinocytes. Three popular hypotheses have been proposed to explain basal keratinocyte regeneration and epidermal homeostasis: 1) asymmetric division (stem-transit amplifying cell); 2) populational asymmetry (progenitor cell with stochastic fate); and 3) populational asymmetry with stem cells. In this study, we investigated lineage dynamics using these hypotheses with a 3D agent-based model of the epidermis. The model simulated the growth and maintenance of the epidermis over three years. The offspring of each proliferative cell was traced. While all lineages were preserved in asymmetric division, the vast majority were lost when assuming populational asymmetry. The third hypothesis provided the most reliable mechanism for self-renewal by preserving genetic heterogeneity in quiescent stem cells, and also inherent mechanisms for skin ageing and the accumulation of genetic mutation.
Subject(s)
Cell Differentiation , Cell Lineage , Epidermal Cells , Keratinocytes/cytology , Models, Biological , Skin/cytology , Stem Cells/cytology , Cell Proliferation , Cells, Cultured , Humans , Regeneration/physiologyABSTRACT
BACKGROUND: Skin ageing represents an inevitable physiological consequence of getting older but the impact on personal health and wellbeing can be significant, and therefore considerable efforts have been made to understand the biology and pathophysiology of skin ageing to try to identify new targets that might offer therapeutic intervention and prevention. OBJECTIVES: This study was designed to identify differences at the gene expression level between young and old, sun-exposed and sun-protected skin. METHODS: We generated transcriptomic data from young and old skin from sun-exposed and sun-protected sites (10 samples of each) using HG-U133 Plus 2.0 Affymetrix GeneChips. The data were analysed using hierarchical clustering, theme analysis and interaction mapping to identify regulated pathways, processes and potential targets for therapy. RESULTS: With 54,613 probe sets on the GeneChip, 2731 significant differences would be expected by chance (at P = 0·05), but we noted that 13,640 probe sets were significantly different comparing young arm skin vs. older arm skin (photoageing), and 7215 probe sets were significant for the young buttock vs. older buttock comparison (intrinsic ageing). In both types of ageing there was reduced expression of many genes implicated in lipid biosynthesis and epidermal differentiation with functional relevance to skin barrier integrity and maintenance. Increased expression of genes contributing to oxidative stress and decreased expression of antioxidant defences were also common to both types of ageing. Differences between intrinsic ageing and photoageing were mainly noted in extracellular matrix gene expression with reduced expression of interstitial collagen genes in intrinsic ageing and increased expression of elastic tissue genes in photoageing. CONCLUSIONS: Collectively, the data identified new biomarkers of aged skin, particularly involving abnormalities of proteases, matrix proteins and inflammation. These findings offer the prospect of new and more specific targets for therapeutic development based on an improved understanding of the biology of skin ageing.
Subject(s)
Gene Expression Profiling/methods , Skin Aging/radiation effects , Sunlight , Ultraviolet Rays , Animals , Biomarkers/metabolism , Female , Humans , Middle Aged , Oligonucleotide Array Sequence Analysis , Skin Aging/genetics , Time Factors , Young AdultABSTRACT
There is an urgent need to validate in vitro human skin models for use in safety testing. An important component of validation is characterizing the metabolizing capacity of these models. We report comparison of the expression of 139 genes encoding xenobiotic metabolizing enzymes in the EpiDerm model and human skin. In microarray analysis, the expression of 87% of the genes was consistent between the EpiDerm model and human skin indicating the presence of similar metabolic pathways suggesting commonality in function. Analysis of EpiDerm models constructed from four donors showed highly comparable expression of xenobiotic metabolizing genes demonstrating reproducibility of the model. Overall, the expression of Phase II enzymes appeared to be more pronounced in human skin and the EpiDerm model than that of Phase I enzymes, consistent with the role of skin in detoxification of xenobiotics. Though the basal expression of CYPs in particular was low in EpiDerm, significant induction of CYP1A1/1B1 activity was observed following treatment with 3-methylcholanthrene. These results indicate that the xenobiotic metabolizing capacity of the EpiDerm model appears to be representative of human skin. Models such as EpiDerm provide a valuable in vitro approach for evaluation of metabolism and toxicity of cutaneous exposures to xenobiotics.
Subject(s)
Epidermis/metabolism , Gene Expression/drug effects , Models, Biological , Skin/metabolism , Xenobiotics/metabolism , Adolescent , Biotransformation , Cytochrome P-450 CYP1A1/metabolism , Cytochrome P-450 Enzyme System/metabolism , Enzyme Induction/drug effects , Epidermis/drug effects , Epidermis/enzymology , Female , Glucuronosyltransferase/metabolism , Glutathione Transferase/metabolism , Humans , In Vitro Techniques , Inactivation, Metabolic , Oligonucleotide Array Sequence Analysis , Skin/drug effects , Skin/enzymology , Xenobiotics/toxicity , Young AdultABSTRACT
Recent time-resolved differential transmission and Faraday rotation measurements of long-lived electron-spin coherence in quantum wells displayed intriguing parametric dependencies. For their understanding we formulate a microscopic theory of the optical response of a gas of optically incoherent excitons whose constituent electrons retain spin coherence, under a weak magnetic field applied in the quantum well's plane. We define a spin beat susceptibility and evaluate it in linear order of the exciton density. Our results explain the many-body physics underlying the basic features observed in the experimental measurements.
ABSTRACT
We present a theoretical analysis for laser cooling of bulk GaAs based on a microscopic many-particle theory of absorption and luminescence of a partially ionized electron-hole plasma. Our cooling threshold analysis shows that, at low temperatures, the presence of the excitonic resonance in the luminescence is essential in competing against heating losses. The theory includes self-consistent energy renormalizations and line broadenings from both instantaneous mean-field and frequency-dependent carrier-carrier correlations, and it is applicable from the few-Kelvin regime to above room temperature.
Subject(s)
Bell Palsy/diagnosis , Acyclovir/administration & dosage , Acyclovir/analogs & derivatives , Acyclovir/therapeutic use , Administration, Oral , Adolescent , Adult , Age Factors , Anti-Inflammatory Agents/administration & dosage , Anti-Inflammatory Agents/therapeutic use , Bell Palsy/classification , Bell Palsy/drug therapy , Bell Palsy/epidemiology , Child , Female , Follow-Up Studies , Glucocorticoids/administration & dosage , Glucocorticoids/therapeutic use , Humans , Incidence , Male , Prednisone/administration & dosage , Prednisone/therapeutic use , Prodrugs/administration & dosage , Prodrugs/therapeutic use , Sex Factors , Time Factors , Treatment Outcome , Valacyclovir , Valine/administration & dosage , Valine/analogs & derivatives , Valine/therapeutic useABSTRACT
We describe a reflection scheme that allows Bragg-spaced semiconductor quantum wells to be used to trap, store, and release light. We study the temporal and spectral distortion of delayed light pulses and show that this geometry allows multibit delays and offers a high degree of distortion compensation.
ABSTRACT
A novel design of an IR photodetector operating at wavelengths around 10 microm is presented. It is based on a three-level quantum coherence effect in semiconductor quantum dots as measured in balanced-homodyne detection in a Mach-Zehnder interferometer. The advantage of this design is the combination of room-temperature operation and fast response time, whereas the major drawback is the high noise-equivalent power.
Subject(s)
Computer-Aided Design , Equipment Failure Analysis/methods , Models, Chemical , Quantum Dots , Spectrophotometry, Infrared/instrumentation , Spectrophotometry, Infrared/methods , Transducers , Computer Simulation , Equipment Design/methods , Photochemistry/instrumentation , Photochemistry/methods , SemiconductorsABSTRACT
The existence of heat-shock protein (HSP) receptors on antigen-presenting cells (APCs) was hypothesized in 1994. The first such receptor, CD91 or LRP, was identified and characterized in 2000. The pace of attribution has quickened since and during the last three years alone, six putative HSP receptors have been identified. These include CD40, LOX-1, CD36, Toll-like receptor-2 (TLR-2), TLR-4 and SR-A. The literature on HSP receptors on APCs is critically examined in this review and future directions are imagined.
Subject(s)
Antigen-Presenting Cells/immunology , Antigens, CD/immunology , CD40 Antigens/immunology , Receptors, Cell Surface/immunology , Receptors, LDL/immunology , Animals , Antigen Presentation/immunology , CD36 Antigens , Heat-Shock Proteins/metabolism , Humans , Lipopolysaccharide Receptors/immunology , Low Density Lipoprotein Receptor-Related Protein-1 , Receptors, Immunologic/immunology , Receptors, Oxidized LDL , Receptors, Scavenger , Scavenger Receptors, Class A , Scavenger Receptors, Class E , Toll-Like Receptor 2ABSTRACT
We report an experimental demonstration and theoretical analysis of electromagnetically induced transparency in a GaAs quantum well, in which the absorption of an exciton resonance is reduced by more than twentyfold. The destructive quantum interference in this scheme is set up by a control pulse that couples to a resonance of biexcitons. These studies illustrate that many-particle interactions, which are inherent in semiconductors and are often detrimental to quantum coherences, can also be harnessed to manipulate these coherences.
ABSTRACT
We propose and analyze a novel scheme to realize electromagnetically induced transparency (EIT) via robust electron spin coherence in semiconductor quantum wells. This scheme uses light hole transitions in a quantum well waveguide to induce electron spin coherence in the absence of an external magnetic field. For certain polarization configurations, the light hole transitions form a crossed double-V system. EIT in this system is strongly modified by a coherent wave mixing process induced by the electron spin coherence.
Subject(s)
ATP-Binding Cassette Transporters , Antimalarials/pharmacology , Chloroquine/pharmacology , Membrane Proteins/genetics , Plasmodium falciparum/drug effects , Polymorphism, Genetic , Protozoan Proteins/genetics , Animals , Drug Resistance/genetics , Gabon , Genetic Markers , Humans , Membrane Transport Proteins , Mutation , Plasmodium falciparum/genetics , Polymerase Chain Reaction , Polymorphism, Restriction Fragment LengthABSTRACT
Increasing resistance of Plasmodium falciparum to antimalarial drugs presents a major risk factor for people living in endemic areas of tropical Africa. In Lambaréné, Gabon, regular surveillance of chloroquine sensitivity of P. falciparum in vitro has been carried out since 1992 using the WHO standard microtest. Results indicated that from 1994 onwards chloroquine resistance in vitro decreased significantly and that by 2000, about 70% of parasite isolates seemed to be sensitive to chloroquine in vitro. In 2001, we conducted a clinical study to reassess the efficacy of chloroquine in vivo for the treatment of uncomplicated P. falciparum malaria. Twenty-six patients aged 4-15 years were included in this study. Most unexpectedly, the study demonstrated high-grade resistance to chloroquine in vivo (failure rate on day 28 of 100%). As a consequence, tests of parasite susceptibility to chloroquine in vitro were repeated using the same protocol except for the replacement of previously used commercially available predosed WHO culture plates by independently dosed plates. All tested P. falciparum isolates were highly resistant to chloroquine, correlating well with our clinical findings. We concluded that high level resistance of P. falciparum to chloroquine persists in the study area. Neglect or absence of quality controls of essential test material can lead to invalid study results and wrong conclusions and should always be suspected in the case of major fluctuations in the sensitivity patterns of an antimalarial drug in vitro. In addition, our results highlight the supreme value of tests in vivo in providing reliable estimates of the efficacy of an antimalarial in a specific area.
Subject(s)
Antimalarials/therapeutic use , Chloroquine/therapeutic use , Malaria, Falciparum/drug therapy , Plasmodium falciparum/drug effects , Adolescent , Animals , Child , Child, Preschool , Drug Resistance , Gabon , Humans , Risk FactorsABSTRACT
We report the experimental observation of coherently coupled heavy-hole-light-hole Stark shifts, i.e., light-hole exciton shifts under heavy-hole exciton pumping conditions, in InGaAs quantum wells. The theoretical analysis of the data is based on a full many-body approach (dynamics-controlled truncation formalism) in the third-order nonlinear optical regime. It is shown that the Stark shift data can be interpreted as strong evidence of suitably defined nonradiative intervalence band coherences in a semiconductor quantum well. Hence, the observations establish a semiconductor analog of Raman coherences in three-level atoms.
ABSTRACT
In a Government/Industry/Academic partnership to evaluate alternative approaches to carcinogenicity testing, 21 pharmaceutical agents representing a variety of chemical and pharmacological classes and possessing known human and or rodent carcinogenic potential were selected for study in several rodent models. The studies from this partnership project, coordinated by the International Life Sciences Institute, provide additional data to better understand the models' limitations and sensitivity in identifying carcinogens. The results of these alternative model studies were reviewed by members of Assay Working Groups (AWG) composed of scientists from government and industry with expertise in toxicology, genetics, statistics, and pathology. The Tg.AC genetically manipulated mouse was one of the models selected for this project based on previous studies indicating that Tg.AC mice seem to respond to topical application of either mutagenic or nonmutagenic carcinogens with papilloma formation at the site of application. This communication describes the results and AWG interpretations of studies conducted on 14 chemicals administered by the topical and oral (gavage and/or diet) routes to Tg.AC genetically manipulated mice. Cyclosporin A, an immunosuppresant human carcinogen, ethinyl estradiol and diethylstilbestrol (human hormone carcinogens) and clofibrate, an hepatocarcinogenic peroxisome proliferator in rodents, were considered clearly positive in the topical studies. In the oral studies, ethinyl estradiol and diethylstilbestrol were negative, cyclosporin was considered equivocal, and results were not available for the clofibrate study. Of the 3 genotoxic human carcinogens (phenacetin, melphalan, and cyclophosphamide), phenacetin was negative by both the topical and oral routes. Melphalan and cyclophosphamide are, respectively, direct and indirect DNA alkylating agents and topical administration of both caused equivocal responses. With the exception of clofibrate, Tg.AC mice did not exhibit tumor responses to the rodent carcinogens that were putative human noncarcinogens, (di(2-ethylhexyl) phthalate, methapyraline HCl, phenobarbital Na, reserpine, sulfamethoxazole or WY-14643, or the nongenotoxic, noncarcinogen, sulfisoxazole) regardless of route of administration. Based on the observed responses in these studies, it was concluded by the AWG that the Tg.AC model was not overly sensitive and possesses utility as an adjunct to the battery of toxicity studies used to establish human carcinogenic risk.