bluuebunny/crossref_metadata_2025 huggingface dataset:
Tetracycline Derivative Minocycline Inhibits Autophagy and Inflammation in Concanavalin-A-Activated Human Hepatoma Cells
Authors: Desjarlais Michel , Pratt Jonathan , Lounis Amine , Mounier Catherine , Haidara Khadidja , Annabi Borhane
Published: March 2014

Inhibition of soluble matrix metalloproteinase (MMP) activity is among the non-antibiotic cellular effects exerted by the anti-inflammatory tetracycline derivative minocycline. The impact of minocycline on the signal transduction functions of membrane-bound MMPs is however unknown. We assessed minocycline in a concanavalin-A (ConA)-activated human HepG2 hepatoma cell model, a condition known to increase the expression of membrane type-1 MMP (MT-MMP) and to trigger inflammatory and autophagy processes. We found that minocycline inhibited ConA-induced formation of autophagic acidic vacuoles, green fluorescent microtubule-associated protein 1 light chain 3 (GFP-LC3) puncta formation, gene and protein expression of autophagy biomarker BCL2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3), invasion biomarker MT1-MMP, and inflammation biomarker cyclooxygenase (COX)-2. Gene silencing of MT1-MMP abrogated ConA-induced formation of autophagic acidic vacuoles and ConA-induced expressions of BNIP3 and COX-2. Minocycline was also shown to inhibit ConA-induced signal transducer and activator of transcription 3 (STAT3) phosphorylation as well as gene expression of NANOS1, a biomarker believed to colocalize with MT1-MMP and the specific silencing of which further inhibited ConA-induced STAT3 phosphorylation. Collectively, our data demonstrate that part of minocycline's effects on autophagy could be exerted through the inhibition of MT1-MMP signaling functions, which contribute to the autophagy and inflammatory phenotype of ConA-activated HepG2 cells.
Filtrations on instanton homology
Authors: Kronheimer Peter B. , Mrowka Tomasz S.
Published: March 2014

In earlier work of the authors, the Khovanov complex of a knot or link appeared as the first page in a spectral sequence abutting to the instanton homology. The quantum and (co)homological gradings on Khovanov homology do not survive as gradings, but we show that they survive as filtrations.
Biochemical and Hematologic Parameters for Children in the Middle Belt of Ghana
Authors: Dosoo David K. , Asante Kwaku P. , Kayan Kingsley , Adu-Gyasi Dennis , Osei-Kwakye Kingsley , Mahama Emmanuel , Danso Samuel , Amenga-Etego Stephen , Bilson Philip , Koram Kwadwo A. , Owusu-Agyei Seth
Published: March 2014

Reference values derived from developed countries are used in many countries in Africa for interpretation of laboratory results obtained during routine healthcare and clinical trials. Use of locally derived reference values has been recommended. The purpose of the study was to establish age- and sex-specific reference values for children in the middle belt of Ghana. Reference values were determined for 21 biochemical and 18 hematologic parameters by using Clinical and Laboratory Standards Institute C28-A3 guidelines in a sample of 1,442 healthy children. Hemoglobin, hematocrit, mean cell volume, erythrocytes, urea, and creatinine were lower when compared with values from northern countries but alanine aminotransferase, aspartate aminotransferase, and total bilirubin were higher. A panel of locally relevant age- and sex-specific reference values was established for commonly used biochemical and hematologic tests in children in the middle part of Ghana. This will help in interpretation of laboratory results for clinical management of patients, screening, and safety monitoring during clinical trials.
Dosing of Praziquantel by Height in Sub-Saharan African Adults
Authors: Palha De Sousa Chiquita A. , Brigham Tracy , Chasekwa Bernard , Mbuya Mduduzi N. N. , Tielsch James M. , Humphrey Jean H. , Prendergast Andrew J.
Published: March 2014

The cornerstone of schistosomiasis control is mass praziquantel treatment in high prevalence areas. Adults are an important target population, given increasing recognition of the burden of male and female genital schistosomiasis. However, use of weighing scales to calculate praziquantel dosing in rural areas can be challenging. For school-age children, the World Health Organization (WHO) has approved a dose pole to simplify praziquantel dosing based on height. We modified the pediatric dose pole by adding two height categories and incorporating a simple overweight/obesity adjustment, for simplified mass treatment of adults in sub-Saharan Africa. Using the rural Zimbabwean Demographic and Health Survey data, we show that the modified dose pole with body mass index adjustment would result in > 98% of adults receiving an acceptable dose (30–60 mg/kg), with only 1.4% and 0.3% receiving an inadequate dose (< 30 mg/kg) or high dose (> 60 mg/kg), respectively. An adult dose pole may provide a more feasible alternative to weighing scales in community-based praziquantel treatment programs.
Brucellosis in Dairy Cattle and Goats in Northern Ecuador
Authors: Poulsen Keith P. , Hutchins Frank T. , McNulty Chase M. , Tremblay Marlène , Zabala Carmen , Barragan Veronica , Lopez Luis , Trueba Gabriel , Bethel Jeffrey W.
Published: March 2014

The purpose of this study was to conduct a convenience study for brucellosis prevalence in dairy-producing animals in northern Ecuador. In total, 2,561 cows and 301 goats were tested. Cattle sera were tested using the Rose Bengal card antigen test (RBCT), yielding an overall apparent prevalence of 5.5% (95% confidence interval [95% CI] = 4.7–6.5%) and true prevalence of 7.2% (95% CI = 6.0–8.5%). Prevalence varied by herd size and was highest in larger commercial herds. Polymerase chain reaction was used to test goat milk and lymph nodes, resulting in 9% and 8% positivity, respectively. The RBCTs from goat sera yielded an adjusted true prevalence of 17.8% (95% CI = 6.2–44.2%). Our findings are similar to other overall prevalence estimates for dairy herds but show higher prevalence in commercial herds compared with small groups (less than five animals). We also identify urban milking goats living in metropolitan Quito as a potential source of zoonosis.
Response to the Critique by Hahn and Others Entitled “Conservation and Malaria in the Brazilian Amazon”
Authors: Valle Denis
Published: March 2014

Hahn and others have recently criticized our study, “Conservation efforts may increase malaria burden in the Brazilian Amazon,” suggesting that results were flawed because of methodological limitations. Here, we briefly comment on some of their claims, showing that (1) several of their criticisms are misleading and others are incorrect, (2) they heavily criticize methods that they themselves have previously used, and (3) they selectively highlight some findings while ignoring others. We end this rebuttal by suggesting a way forward in this debate.
Mass deposition fluxes of Saharan mineral dust to the tropical northeast Atlantic Ocean: an intercomparison of methods
Authors: Niedermeier N. , Held A. , Müller T. , Heinold B. , Schepanski K. , Tegen I. , Kandler K. , Ebert M. , Weinbruch S. , Read K. , Lee J. , Fomba K. W. , Müller K. , Herrmann H. , Wiedensohler A.
Published: March 2014

Abstract. Mass deposition fluxes of mineral dust to the tropical northeast Atlantic Ocean were determined within this study. In the framework of SOPRAN (Surface Ocean Processes in the Anthropocene), the interaction between the atmosphere and the ocean in terms of material exchange were investigated at the Cape Verde atmospheric observatory (CVAO) on the island Sao Vicente for January 2009. Five different methods were applied to estimate the deposition flux, using different meteorological and physical measurements, remote sensing, and regional dust transport simulations. The set of observations comprises micrometeorological measurements with an ultra-sonic anemometer and profile measurements using 2-D anemometers at two different heights, and microphysical measurements of the size-resolved mass concentrations of mineral dust. In addition, the total mass concentration of mineral dust was derived from absorption photometer observations and passive sampling. The regional dust model COSMO-MUSCAT was used for simulations of dust emission and transport, including dry and wet deposition processes. This model was used as it describes the AOD's and mass concentrations realistic compared to the measurements and because it was run for the time period of the measurements. The four observation-based methods yield a monthly average deposition flux of mineral dust of 12–29 ng m−2 s−1. The simulation results come close to the upper range of the measurements with an average value of 47 ng m−2 s−1. It is shown that the mass deposition flux of mineral dust obtained by the combination of micrometeorological (ultra-sonic anemometer) and microphysical measurements (particle mass size distribution of mineral dust) is difficult to compare to modeled mass deposition fluxes when the mineral dust is inhomogeneously distributed over the investigated area.
SO2 noontime peak phenomenon in the North China Plain
Authors: Xu W. Y. , Zhao C. S. , Ran L. , Lin W. L. , Yan P. , Xu X. B.
Published: March 2014

Abstract. Frequent SO2 noontime peak phenomenon was discovered in a detailed analysis on the SO2 concentrations in the North China Plain (NCP). The possible causes and their contributions are analysed. The impacts of such a phenomenon on the sulphur cycle were studied and the implications of the phenomenon for atmospheric chemistry, cloud physics and climate were discussed. Different from the common SO2 diurnal patterns with high nighttime concentrations, NCP witnessed high frequencies of SO2 noontime peaks, with an occurrence frequency of 50–72% at the four stations. Down-mixing of elevated pollution layers, plume transport processes, mountain-valley-winds and fog/high RH haze events were the possible causes. The contribution of each process varies from each other and from station to station, however, neither of those four processes can be neglected. SO2 peaks occurring during noontime instead of nighttime will lead to a 13–35% increase in sulphur dry deposition, 9–23% increase in gas phase oxidation and 8–33% increase in aqueous phase conversions, which will increase the hygroscopicity and the light scattering of aerosols, thus having important impacts on atmospheric chemistry, cloud physics and climate.
Reconciling aerosol light extinction measurements from spaceborne lidar observations and in-situ measurements in the Arctic
Authors: Tesche M. , Rastak N. , Charlson R. J. , Glantz P. , Zieger P. , Hansson H.-C.
Published: March 2014

Abstract. In this study we investigate to what degree it is possible to reconcile continuously recorded particle light extinction coefficients derived from dry in-situ measurements at Zeppelin station (78.92° N, 11.85° E, 475 m a.s.l.) at Ny-Ålesund, Svalbard, that are recalculated to ambient relative humidity, and simultaneous ambient observations with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. To our knowledge, this represents the first study that compares spaceborne lidar measurements to optical aerosol properties from short-term in-situ observations (averaged over 5 h) on a case-by-case basis. Finding suitable comparison cases requires an elaborate screening and matching of the CALIOP data with respect to the location of the Zeppelin station as well as in the selection of temporal and spatial averaging intervals for both the ground-based and spaceborne observations. Trustworthy reconciliation of these data cannot be achieved with the closest approach method that is often used in matching CALIOP observations to those taken at ground sites due to the transport pathways of the air parcels that were sampled. The use of trajectories allowed us to establish a connection between spaceborne and ground-based observations for 57 individual overpasses out of a total of 2018 that occurred in our region of interest around Svalbard (0 to 25° E; 75 to 82° N) in the considered year of 2008. Matches could only be established during winter and spring, since the low aerosol load during summer in connection with the strong solar background and the high occurrence rate of clouds strongly influences the performance and reliability of CALIOP observations. Extinction coefficients in the range from 1 to 100 Mm−1 were found for successful matches with an agreement of a factor of 1.85 (median value for a range from 0.38 to 17.9) between the findings of in-situ and spaceborne observations (the latter being generally larger than the former). The remaining difference is likely to be due to the natural variability in aerosol concentration and ambient relative humidity, an insufficient representation of aerosol particle growth in the used hygroscopicity model, or a misclassification of aerosol type (i.e., choice of lidar ratio) in the CALIPSO retrieval.
Seasonal logging, process response, and geomorphic work
Authors: Mohr C. H. , Zimmermann A. , Korup O. , Iroumé A. , Francke T. , Bronstert A.
Published: March 2014

Abstract. Deforestation is a prominent anthropogenic cause of erosive overland flow and slope instability, boosting rates of soil erosion and concomitant sediment flux. Conventional methods of gauging or estimating post-logging sediment flux often focus on annual timescales but overlook potentially important process response on shorter intervals immediately following timber harvest. We resolve such dynamics with non-parametric quantile regression forests (QRF) based on high-frequency (3 min) discharge measurements and sediment concentration data sampled every 30–60 min in similar-sized (∼0.1 km2) forested Chilean catchments that were logged during either the rainy or the dry season. The method of QRF builds on the random forest algorithm, and combines quantile regression with repeated random sub-sampling of both cases and predictors. The algorithm belongs to the family of decision-tree classifiers, which allow quantifying relevant predictors in high-dimensional parameter space. We find that, where no logging occurred, ∼80% of the total sediment load was transported during extremely variable runoff events during only 5% of the monitoring period. In particular, dry-season logging dampened the relative role of these rare, extreme sediment-transport events by increasing load efficiency during more efficient moderate events. We show that QRFs outperform traditional sediment rating curves (SRCs) in terms of accurately simulating short-term dynamics of sediment flux, and conclude that QRF may reliably support forest management recommendations by providing robust simulations of post-logging response of water and sediment fluxes at high temporal resolution.
On the analytic approximation of bulk collision rates of non-spherical hydrometeors
Authors: Seifert A. , Blahak U. , Buhr R.
Published: March 2014

Abstract. Analytic approximations of the binary collision rates of hydrometeors are derived for use in bulk microphysical parameterizations. Special attention is given to non-spherical hydrometeors like raindrops and snowflakes. The terminal fall velocity of these particles cannot be sufficiently well approximated by power-law relations which are used in most microphysical parameterizations, and therefore an improved formulation is needed. The analytic approximations of the bulk collision rates given in this paper are an alternative to look-up tables and can replace the Wisner approximation, which is used in many atmospheric models.
The anomalous low and high temperatures of 2012 over Greece – an explanation from a meteorological and climatological perspective
Authors: Tolika K. , Maheras P. , Pytharoulis I. , Anagnostopoulou C.
Published: March 2014

Abstract. 2012 was the hottest year in Greece on the basis of the available record dating back to 1958, displaying at the same time the widest annual temperature range. During the summer and autumn months, numerous regions in the domain of study experienced record-breaking maximum and minimum temperatures. Conversely, the winter period was particularly cold and January one of the coldest months over the last 55 yr. The analysis of the cold period indicates that the synoptic conditions resemble the positive phase of the Eastern Mediterranean Pattern (EMP). The predominance of these cool conditions seems to be related primarily to an intense NNW or NNE atmospheric circulation, as a consequence of the positive EMP phase. Moreover, the reduction in the floating sea ice emerges as a key driver of the formation of a low-pressure pattern and the reinforcement of the trough south of Scandinavia, which in turn strengthened the Siberia High east of the trough. This reinforcement resulted in a blocking pattern and in favorable conditions for the EMP formation. The atmospheric circulation during the prolonged high-temperature period resembles, respectively, the negative phase of North Sea–Caspian Pattern teleconnection. The observed positive pole, in conjunction with the strong southwestern circulation, results in temperature increases and in the development of a smooth pressure field that contributes to the weakening of the Etesian winds and therefore to calm conditions over the continental areas.
Application of GA–SVM method with parameter optimization for landslide development prediction
Authors: Li X. Z. , Kong J. M.
Published: March 2014

Abstract. Prediction of the landslide development process is always a hot issue in landslide research. So far, many methods for landslide displacement series prediction have been proposed. The support vector machine (SVM) has been proved to be a novel algorithm with good performance. However, the performance strongly depends on the right selection of the parameters (C and γ) of the SVM model. In this study, we present an application of genetic algorithm and support vector machine (GA–SVM) method with parameter optimization in landslide displacement rate prediction. We selected a typical large-scale landslide in a hydro-electrical engineering area of southwest China as a case. On the basis of analyzing the basic characteristics and monitoring data of the landslide, a single-factor GA–SVM model and a multi-factor GA–SVM model of the landslide were built. Moreover, the models were compared with single-factor and multi-factor SVM models of the landslide. The results show that the four models have high prediction accuracies, but the accuracies of GA–SVM models are slightly higher than those of SVM models, and the accuracies of multi-factor models are slightly higher than those of single-factor models for the landslide prediction. The accuracy of the multi-factor GA–SVM models is the highest, with the smallest root mean square error (RMSE) of 0.0009 and the highest relation index (RI) of 0.9992.
Small impact of surrounding oceanic conditions on 2007–2012 Greenland Ice Sheet surface mass balance
Authors: Noël B. , Fettweis X. , van de Berg W. J. , van den Broeke M. R. , Erpicum M.
Published: March 2014

Abstract. During recent summers (2007–2012), several surface melt records were broken over the Greenland Ice Sheet (GrIS). The extreme summer melt resulted in part from a persistent negative phase of the North-Atlantic Oscillation (NAO), favouring warmer than normal conditions over the GrIS. In addition, it has been suggested that significant anomalies in sea ice cover (SIC) and sea surface temperature (SST) may partially explain recent anomalous GrIS surface melt. To assess the impact of 2007–2012 SIC and SST anomalies on GrIS surface mass balance (SMB), a set of sensitivity experiments was carried out with the regional climate model MAR. These simulations suggest that changes in SST and SIC in the seas surrounding Greenland do not significantly impact GrIS SMB, due to the katabatic winds blocking effect. These winds are strong enough to prevent oceanic near-surface air, influenced by SIC and SST variability, from penetrating far inland. Therefore, the ice sheet SMB response is restricted to coastal regions, where katabatic winds are weaker. However, anomalies in SIC and SST could have indirectly affected the surface melt by changing the general circulation in the North Atlantic region, favouring more frequent warm air advection to the GrIS.
Solving Steady Flow of a Third-Grade Fluid in a Porous Half Space via Normal and Modified Rational Christov Functions Collocation Method
Authors: Parand Kourosh , Hajizadeh Emran
Published: March 2014

The present study is an attempt to find a solution for steady flow of a third-grade fluid by utilizing spectral methods based on rational Christov functions. This problem is described as a nonlinear twopoint boundary value problem. The following method tries to solve the problem on the infinite domain without truncating it to a finite domain and transforms the domain of the problem to a finite domain. Researchers in this try to solve the problem by using anew modified rational Christov functions and normal rational Christov function. Finally, the findings of the current study, i. e., proposal methods, numerical out cames and other methods were compared with each other.
A Rationale for Irrationals: An Unintended Exploration of e
Authors: Wasserman Nicholas H.
Published: March 2014

The practice of problem posing is as important to develop as problem solving. The resulting explorations can be mathematically rich.
Working the System
Authors: Berks Darla R. , Vlasnik Amber N.
Published: March 2014

Two teachers discuss the planning and observed results of an introductory problem to help students nail a conceptual approach to solving systems of equations.
Measuring Biodiversity with Probability
Authors: Duncan Sarah I. , Lenhart Suzanne , Sturner Kelly K.
Published: March 2014

More and more, teachers are asked to make connections between the STEM disciplines—science, technology, engineering, and mathematics—while also addressing state standards. Mathematics is an underappreciated but important tool for the life sciences, from mathematically modeling biological processes to making sense of biological data. The activity presented here was designed for a Girls in Science camp, held at Tremont, Tennessee, in the Great Smoky Mountains National Park. The camp is designed to give local girls entering eighth grade a chance to become familiar with the natural world by doing hands-on research in the park. This particular exercise was designed to show the value of mathematics for quantifying and interpreting biodiversity data that the girls had collected.
Solve It! Picking and Packing Strawberries
Authors: Bair Sherry L. , Cady JoAnn
Published: March 2014

To elicit creative student thinking, this open-ended problem asks solvers to calculate fractional parts of crates of strawberries.
Palette of Problems – March 2014
Authors: Amidon Joel , Roscoe Matt
Published: March 2014

A monthly set of problems is aimed at a variety of ability levels.
Decimal Fractions: An Important Point
Authors: Martinie Sherri L.
Published: March 2014

Teachers who are skilled at recognizing students' misconceptions about decimals are better equipped to make instructional decisions that build on these ideas.
Math for Real: How Much Time Will Lena Save?
Authors: Miltner Dan
Published: March 2014

This problem ties in the Pythagorean theorem while two people walk around or across a park.
Problem: Area Beyond the Formula
Authors: Dean Chrystal
Published: March 2014

This variation of Simon's (1995) rectangle exploration will have students investigating area in a conceptual manner that goes beyond tiling and formulas. Each month, elementary school teachers are given a problem along with suggested instructional notes; are asked to use the problem in their own classrooms; and are encouraged to report solutions, strategies, reflections, and misconceptions to the journal audience.
Solutions: Playing Basketball
Authors: Smith Jeffrey
Published: March 2014

Articles in this department showcase students' in-depth thinking and work on problems previously published in Teaching Children Mathematics. This month's scenario challenges students to consider elapsed time and requires them to convert between different units of time measure.
The Mathematics of Tiling
Authors: Kurz Terri L.
Published: March 2014

People who lay tile for a living use mathematics every day to decide how much tile, grout, and other supplies are required to complete each job. Measurement and geometry are an integral part of designing tile patterns. Collections of short activities focus on a monthly theme that includes four activities each for grade bands K–2, 3–4, and 5–6 and aims for an inquiry or problem-solving orientation.
Connecting the Threads of Area and Perimeter
Authors: Hede Jordan T. , Bostic Jonathan D.
Published: March 2014

See how sixth-grade students design and create quilt squares for this geometry project.
Oki-Doku: Number Puzzles
Authors: Gomez Cristina , Novak Dani
Published: March 2014

Consider using these problems to help students develop number and operation sense in a simple and fun way.
Recompositions territoriales autochtones en milieu urbain
Authors: Sepúlveda Bastien
Published: March 2014

Après la conquête de leur territoire par l’armée chilienne à la fin duxixe siècle, les Mapuches ont été soumis à un intense processus de migration qui les a menés principalement vers les grandes villes du Chili. Ce phénomène n’a cessé de prendre de l’ampleur au fil des ans, au point que la société mapuche est aujourd’hui devenue majoritairement urbaine ; en effet, d’après les données du recensement de 2002, près de 65 % de la population autochtone du Chili résiderait en ville. Si cette forme de mobilité semble certes pouvoir être interprétée dans la perspective d’un départ contraint, elle traduit en même temps une incroyable capacité d’adaptation à une réalité changeante. À partir d’un travail mené avec des associations mapuches de l’agglomération de Concepción, dans le centre du Chili, cet article s’intéresse aux modes d’inscription de l’identité mapuche dans ce nouvel espace qu’est la ville et à la manière dont celui-ci se trouve finalement intégré à la structure territoriale autochtone.
Membranes linked by trans-SNARE complexes require lipids prone to non-bilayer structure for progression to fusion
Authors: Zick Michael , Stroupe Christopher , Orr Amy , Douville Deborah , Wickner William T
Published: March 2014

Like other intracellular fusion events, the homotypic fusion of yeast vacuoles requires a Rab GTPase, a large Rab effector complex, SNARE proteins which can form a 4-helical bundle, and the SNARE disassembly chaperones Sec17p and Sec18p. In addition to these proteins, specific vacuole lipids are required for efficient fusion in vivo and with the purified organelle. Reconstitution of vacuole fusion with all purified components reveals that high SNARE levels can mask the requirement for a complex mixture of vacuole lipids. At lower, more physiological SNARE levels, neutral lipids with small headgroups that tend to form non-bilayer structures (phosphatidylethanolamine, diacylglycerol, and ergosterol) are essential. Membranes without these three lipids can dock and complete trans-SNARE pairing but cannot rearrange their lipids for fusion.
Heterostructure Stability: Connections between High Pressure and Epitaxial Growth
Authors: Weinstein B. A. , Gui L. J. , Venkateswaran U. D.
Published: March 2014

The stability of semiconductor epitaxial systems is discussed within a framework that clarifies connections between high pressure observations and 1 atm. growth conditions. Pressure-Raman results on interface mechanical stability in ZnSe/GaAs epilayers, and on phase stability in AlAs/GaAs superlattices are presented. In both cases the interface energetics play an important role. A theoretical analysis within a disordered interface picture offers insights into the occurence and prediction of metastable 1 atm. heterostructures.
Pressure Dependence of the Valence-Band Offset in (GaAs)8/(Al0.3Ga0.7As)12 Short Period Superlattice
Authors: Liu Zhen-xian , Li Guo-hua , Han He-xiang , Wang Zhao-ping , Jiang De-sheng , Ploog Klaus
Published: March 2014

(GaAs)8/(Al0.3Ga0.7As)12 short period superlattice (SPSL) and bulk Al0.3Ga0.7As have been studied by photoluminescence (PL) measurements at liquid nitrogen temperature under nigh pressure up to 3GPa. The pressure coefficients of the direct and indirect gaps in bulk Al0.3Ga0.7As are 86±3 and -15.7±0.7 meV/GPa, respectively. The observed transitions from conduction X-like electrons to heavy hole states in (GaAs)8/(Al0.3Ga0.7As)12 SPSL have an unexpected pressure coefficient, -22±1 meV/GPa, which is interpreted as evidence for a pressure dependence of the valence-band offset (Δ Ev) of approximately 6 meV/GPa. This value is about twice the result of Lambkin et al. Our results show that the pressure coefficient of the valence-band offset in GaAs/AlxGa1-xAs superlattice is dependent not only on aluminum concentration but also on the superlattice structure. Moreover, the fractional conduction- and valence-band offsets of (GaAs)8/(Al0.3Ga0.7As)12 SPSL are also pressure and SL structure dependent.
Magneto-Photoluminescence Study of Be δ-Doped GaAs/AlGaAs Quantum Wells under Hydrostatic Pressure
Authors: Lyapin S. G. , Raymond A. , Vicente P. , Kubisa M. , Sauvajol J. L. , Zekentes K. A. , Hatzopoulos Z.
Published: March 2014

We have performed photoluminescence experiments in magnetic field up to 12 T and under hydrostatic pressure (0-8 kbar), at helium temperature on wide (50 nm) single-side modulation doped GaAs - AlGaAs quantum wells with and without Be acceptor planar doping. Application of pressure reduced free-electron density, resulting in evolution from heterojunction-like to none-doped wide-quantum-well-like behaviour. The observation of the 2D electron to neutral acceptor recombination gave us an unique possibility to eliminate excitonic effects which strongly affect the electron-hole transitions, and consequently, to investigate directly the effective mass of 2DEG during the pressure induced metal-insulator transition.
High Hydrostatic Pressure Effects on Perpendicular Transport in GaAs–AlAs Superlattices
Authors: Aristone F. , Sibille A. , Palmier J. F. , Goutiers B. , Portal J. C. , Mollo F.
Published: March 2014

We report perpendicular transport measurement on a series of GaAs-AlAs superlattices in the presence of applied hydrostatic pressure up to 11Kbar. The calculation of the minibands widths and their relative position was performed taking into account a K.P model, which allowed the determination of the direct or indirect characteristic for each sample. Considering the relative fast rate in energy (approximately 12meV/Kbar) of the Γ miniband relatively to the X states we interpreted the pressure effects with a good qualitative agreement.
Tailoring of the Valence Band Offset in the ZnSe/ZnTe Strained-Layer Superlattices Using Strong Built-in Strain Fields
Authors: Cloitre T. , Briot N. , Briot O. , Gil B. , Boring P. , Ponga B. E. , Aulombard R. L.
Published: March 2014

ZnSe/ZnTe strained-layer short period superlattices have been grown by MOVPE. Using well adapted buffer layers, we could tune the internal built-in strain of the individual layers. We studied both free standing superlattices and strained-layer superlattices lattice matched to ZnTe. We observe that the tuning of the valence band offset by the internal strain can produce a switching of the superlattice band gap from type II e1hh1 to type I e11h1. Photoreflectance investigations enabled us to measure excited state transitions allowing us to obtain the strain free valence band offset with considerable accuracy.
Higher-Interband Transitions in (AlAs)m(GaAs)m Superlattices under High Pressure
Authors: Hitomi Satoshi , Takarabe Ken-ichi , Minomura Sigeru , Kato Hiromu , Watanabe Yasutaka
Published: March 2014

Higher-interband transitions in short period (AlAs)m(GaAs)m superlattices are investigated as a function of layer period and pressure. Quantum confinement effects are observed in the E1 transition. The E1 transition energy increased with decreasing monolayer period. The transition energy approaches that of GaAs for larger monolayer periods (m≥15), and it approaches that of Al0.5Ga0.5As alloy for smaller monolayer periods (m≤4). The pressure coefficient of superlattices with m≥15 is the same as GaAs, but that of superlattices with m≤4 is the same as the Al0.5Ga0.5As alloy.
Optical Properties of (InAs)1/(GaAs)m Strained-Layer Superlattices
Authors: Nakayama Masaaki , Fujita Takashi , Tanaka Isao , Nishimura Hitoshi , Terauchi Hikaru
Published: March 2014

We report the photoluminescence (PL) and absorption (ABS) properties of (InAs)1/(GaAs)
m
strained-layer superlattices with m=7, 10, 20, and 30 monolayers grown on a (001) GaAs substrate by molecular-beam epitaxy. We have clearly observed the ABS bands of the heavy-hole and light-hole excitons associated with the first subbands and the PL band of the heavy-hole exciton. It is found that the exciton energies increase as the GaAs-layer thickness increases. The GaAs-layer-thickness dependence of the Exciton energy is reasonably explained by the calculated results on the basis of an effective-mass approximation including strain effects. In addition, the band-offset energy of the GaAs/InAs heterojunction is discussed.
Amorphization from Quenched High-Pressure Phase at Low Temperatures and High Pressures in Semiconductors
Authors: Tsuji Kazuhiko , Katayama Yoshinori , Koyama Naoe , Imai Motoharu
Published: March 2014

X-ray diffraction for amorphous Si1-x
Ge
x
(0.0≤x≤1.0) and crystalline GaSb has been measured at various pressures up to 13 GPa and temperatures down to 100 K using synchrotron radiation. Pressure-induced phase transitions to metallic phases and amorphizations were observed. The behavior of phase transitions strongly depends on paths in a pressure-temperature phase diagram. The high-pressure phase was quenched on release of pressure at low temperature. Amorphization from a quenched high-pressure phase occurred for a-Si1-x
Ge
x
and GaSb when the temperature was elevated at low pressure. These results are discussed in connection with the pressure dependence of potential barriers for the phase transitions.
Pressure as a Probe of Deep Levels and Defects in Semiconductors: GaAs, GaP and Their Alloys
Authors: Samara George A.
Published: March 2014

Measurements of the effects of pressure on the thermal electron emission rate and capture cross section for a variety of deep electronic levels in GaAs, GaP and their alloys have yielded the pressure dependences of the energies of these levels in the bandgaps, allowed evaluation of the breathing mode lattice relaxations accompanying carrier emission or capture by these levels and revealed trends which lead to new insights into the nature of the responsible defects. Emphasis is on deep levels believed to be associated with simple defects. Specifically, results will be summarized for the donor levels of the dominant native defect known as EL2 in GaAs, which is believed to be associated with the arsenic antisite, and on the radiation-induced El and E2 levels in GaAs, GaP and their alloys, which are believed to be due to arsenic (or phosphorous) vacancies. The results are discussed in terms of models for the defects responsible for these deep levels.
Spatial Correlation of Occupied DX Centres in GaAs and its Destruction by Thermal and Optical Excitation
Authors: Dmowski L. H. , Goutiers B. , Maude D. K. , Eaves L. , Portal J. C. , Harris J. J.
Published: March 2014

We have studied the population and depopulation processes of Si-DX levels and the mobility enhancement due to the spatial correlation of charged centres in heavily doped GaAs. The destruction of the correlated occupation of DX centres has been investigated using two methods; (i) optical destruction by sub-bandgap photons, (ii) thermal destruction using time dependent relaxation processes. Depending on the degree of correlation the mobility at a particular temperature and at atmospheric pressure can vary over a range of values for a fixed value of carrier concentration.
Farinfrared Magneto-Optics of the Shallow-Deep Impurity Transitions Using Diamond Anvil Cells
Authors: Dmochowski J .E. , Stradling R. A.
Published: March 2014

High pressure studies of electronic states of impurity donors in GaAs are reported. The diamond anvil high-pressure cell technique is applied to far-infrared magneto-optical experiments. Absorption due to the ls-2p(+) transition for different shallow donor species is investigated in transmission experiments using far-infrared laser radiation at pressures up to 40 kbar. A shallow-deep transition is observed for sulphur, silicon and tin donors close to 30 kbar, resulting in bleaching of the FIR absorption. The transition is similar to that for the Ge donor at 9 kbar observed previously with Unipress cells. Deep states responsible for quenching of FIR absorption are further investigated in photoluminescence experiments. They do not follow either the Γ or X conduction band. All these deep states which are resonant with the conduction band at ambient pressure have the attributes predicted theoretically of highly localized, weakly relaxed states with A1 symmetry associated with substitutional impurities.
Hydrostatic Pressure Dependence of Eg-100 meV Photoluminescence Emissions in n-Type AlGaAs
Authors: Uchida Kazuo , Seguy Patrice , Wong Hoover , Souza Patricia L. , Yu Peter Y. , Weber Eicke R. , Matsumoto Koh
Published: March 2014

The pressure dependence of deep emission bands (occurring at about 100 meV below the band-to-band recombination peak) in two types of n-AlGaAs materials grown by Metal Organic Vapor Phase Epitaxy (MOVPE) and Molecular Beam Epitaxy (MBE) has been measured by Photoluminescence (PL) in order to investigate the origin of these deep emissions. The results indicate that these deep emissions are probably due to transition between a shallow donor and a deep accepter located about 100 meV above the valence band.
Can One Microscopic Model Explain the Different Behavior of Si- and Te-Related DX Centers in AlGaAs?
Authors: Piotrzkowski R. , Litwin-Staszewska E. , Suski T. , Konczewicz L. , Robert J. L.
Published: March 2014

The method of pressure assisted studies of thermostimulated electron emission from resonant DX-levels was used to study the structure of thermal emission from Te in AlxGa1-xAs(x=0.15, 0.2, 0.25). Seven or eight components contributing to the emission process were found, as can be expected considering the possible alloy-splitting effect for a group-VI DX center in the negative-U model. The emission barriers depend on pressure and alloy composition. The possible correspondence between the configurations of DX centers and the different emission components is found, and the estimation of level positions is given. The obtained results are compared with the results for a multiple level structure of the Si-DX center. Both the similarities and differences can be understood on the grounds of a negative-U model of the DX-center.
Hydrostatic Pressure Effects on Self-Trapped Exciton Luminescence in KI
Authors: Nishimura H. , Oguri T. , Tsujimoto T. , Nakayama M. , Kurisu H. , Komatsu T. , Morita S. , Kobayashi M.
Published: March 2014

The effect of hydrostatic pressure up to 1.44 GPa upon the luminescence bands associated with self–trapped excitons (STE's) and impurity (Tl+) in KI has been measured at various temperatures. A sapphire anvil cell with helium as a pressure medium is used. The STE luminescence bands show strong blue shift (0.43 eV/GPa for the σ band), which is much larger than the blue shift of the 1s exciton energy (0.16 eV/GPa). The intensities and half-widths of the STE luminescence bands decrease with pressure. These results are discussed on the basis of the exciton-lattice interaction strength depending on hydrostatic pressure.
Views from the Electronic Structure of (GaAs)n(AlAs)n Short Period Superlattices
Authors: Kamimura Hiroshi , Shibata Gakuei , Nakayama Takashi
Published: March 2014

Very short period superlattices including strained superlattices have recently aroused keen interests as a new class of materials among semiconductor superlattices and have been extensively studied both theoretically and experimentally. In particular, very short period GaAs/AlAs superlattices with (001) interface was one of the highlight topics among various kinds of superlattices for recent several years. A number of first principles band structure and stability calculations have been performed for (GaAs)
n
(AlAs)
n
superlattices with (001) interface, and a number of experimental groups have tested theoretical results. This plenary lecture is devoted to give an overview on the recent remarkable progress in research on the band structures and optical properties of this system. Finally, as a direction in the future prospect of research on this system, the improvement of the band gap problem in the local density approximation and the sample problem is discussed.
Electronic Structure of Strained Superlattices
Authors: Nakayama Takashi
Published: March 2014

Electronic structures and band offsets of zinc-compound (001) strained superlattices are calculated by the first-principles pseudopotential method. It is shown that strain causes large level splitting, the strain-induced light-hole gap appears in some superlattices and strained superlattices become quantum well systems for the states around the fundamental gap. With varying the strain surroundings, the band offset drastically changes due to the energy-level shift by strain and charge transfer at the interface, a mechanism of which is analyzed in order to predict a general feature of the variation of band offset in strained superlattices.
Picosecond Dynamics of Confined Excitons and Their Optical Nonlinearities in CuCl Nanocrystals
Authors: Itoh Tadashi , Iwai Sadayuki , Edamatsu Keiichi , Yano Satoshi , Goto Takenari
Published: March 2014

Optical nonlinearities in confined exciton system were investigated in CuCl nanocrystals embedded in NaCl matrices at 77 K with use of ns and sub-ps laser excitations. Size-dependent excitation photon density necessary for the saturation of the exciton absorption peak under the ns excitation at the exciton resonance showed that the number of excitons per one nanocrystal governs the magnitude of the saturation regardless of the crystal size. Transient absorption change measured under sub-ps band-to-band excitation revealed the strong correlation between the temporal response of the excitonic optical nonlinearities and the formation and decay dynamics of the exciton and biexciton systems in CuCl nanocrystals.
Study on Transient Photoinduced Absorption of One-Dimensional Excitons by Molecular Dynamics
Authors: Ishida Kunio , Itoh Satoshi
Published: March 2014

Transient photoinduced absorption (PA) of one-dimensional (1D) excitons due to exciton-exciton transition is studied. The energy relaxation of the A

g
excitons as a final state of the PA process is taken into account to discuss quantitatively the amount of peak shift in the PA spectra as a result of lattice relaxation. The relation between the relaxation energy of exciton states and the strength of electron-phonon interactions is also studied and it is shown that the PA peak also makes a blue shift except for weak-electron-phonon-coupling cases.
Some Properties of Quantum Wells and Superlattices in Cylindrical Geometry
Authors: Ping Er-Xuan
Published: March 2014

We review some recent studies on the properties of quantum wells and superlattices in a non-traditional geometry, cylindrical geometry. We discuss the potential applications of the structures in the fast electronics and lasers.
Electric Field Dependent Refractive Index of Quantum-Well Structures: Their Measurement and Applications
Authors: Langer Dietrich W. , Maeda Yoshinobu
Published: March 2014

The strong variation of the refractive index (Δn) of multiple quantum wells (MQW) with an externally applied electric field (ΔE) can be exploited in a variety of device structures usable in integrated opto-electronic circuits. Design and fabricational tolerances determine Δn/ΔE as function of wavelength. A method for the experimental control of this parameter and the application of MQW structures in field induced waveguides is provided.
High Efficiency Electroluminescence from Porous Silicon during Anodic Oxidation
Authors: Sakai Tadashi , Suzuki Taketoshi , Zhang Li
Published: March 2014

The Electroluminescence of p- type porous silicon during anodic oxidation (AO) in HCl solution has been investigated quantitatively. A typical EL peak wavelength at maximum intensity during AO was around 690 nm and the external light emitting efficiency at that time (ηm) was 0.12 %. The ηm was nearly proportional to anodic etching (AE) current density (D
AE) and also increased with AE time (t
AE). For the AO conditions, ηm increased abruptly as the AO current density (D
AO) was reduced and it reached a maximum of 0.27% at minimum D
AO condition. Furthermore, it was found that ηm was uniquely described by the AO voltage rise rate (d
V
AO/d
t), which represents the effective injection current density into the PS microstructure surface.
Exciton-Neutral-Donor Complexes in Semiconductor Quantum Dots
Authors: Chen Yimin , Fan Xiwu , Li Qingmian , Zhang Xiqing , Zhao Futan
Published: March 2014

The quantum states of exciton-neutral-donor complexes in semiconductor quantum dots are computed using a numerical matrix-diagonalization scheme. The results predict an increasing binding energy of exciton to neutral donor with decreasing dot size.
Excitonic Spectra in Semiconductor Nanostructures
Authors: Zimmermann Roland
Published: March 2014

Due to the carrier confinement in nanostructures, the Coulomb attraction between electrons and holes is enhanced, and the exciton bound states dominate more than in bulk material. Results from a numerical solution of the Schrödinger equation can be visualized introducing the concept of an “effective dimension”. Further, such refinements as image charge effects, excitons in type-II quantum structures, and inhomogeneous broadening due to interface roughness are discussed.
Light Emission from C2 Fragments Decomposed from C60 during Laser Ablation
Authors: Kasuya A. , Achiba Y. , Nishina Y.
Published: March 2014

Fragmentations of C60 in the laser ablation of C60 film has been analyzed by a space/time resolved optical spectrometry with the resolution of micron in space and ns in time. Observation of light emission with increasing spectral broadening in the period over 1 micro-second suggests that C60 decomposes in a series of fragmentation processes by ejecting C2 molecules in each step. The ejecting processes are found more violent towards later fragmentation events. The result is well explained in our model of laser ablation.
Coherent Raman Spectroscopy and Time-Resolved Emission of CdSe Quantum Dots in Glass
Authors: Jungnickel Volker , Henneberger Fritz , Riblet Phillipe , Hönerlage Bernd
Published: March 2014

This paper reports on experimental results about the electron-phonon coupling in few nm sized CdSe quantum dots (QDs) embedded in a glass matrix. We compare results from non-degenerate four-wave mixing (NDFWM) with those from time resolved photoluminescence (PL). In NDFWM, we report for the first time on a distinct enhancement of |χ(3)|2 for beam detunings near the bulk LO-phonon energy. We extend Yajima's theory on NDFWM1) to the case of an inhomogeneously broadened multi phonon system including Coherent Raman Scattering processes. The theory gives reasonable agreement with the data and enables us to deduce the Huang-Rhys parameter and the relevant relaxation times from the experiment. In PL, the corresponding Franck-Condon progression of the electron-hole (e-h) pair groundstate is clearly resolved. We compare the coupling constants and the homogeneous line widths deduced from both experiments and demonstrate the effect of photostructural changes upon the relaxation times.