bluuebunny/crossref_metadata_2025 huggingface dataset:
Human thymopoiesis produces polyspecific CD8+ α/β T cells responding to multiple viral antigens
Authors: Quiniou Valentin , Barennes Pierre , Mhanna Vanessa , Stys Paul , Vantomme Helene , Zhou Zhicheng , Martina Federica , Coatnoan Nicolas , Barbie Michele , Pham Hang-Phuong , Clémenceau Béatrice , Vie Henri , Shugay Mikhail , Six Adrien , Brandao Barbara , Mallone Roberto , Mariotti-Ferrandiz Encarnita , Klatzmann David
Published: March 2023

T-cell receptors (TCRs) are formed by stochastic gene rearrangements, theoretically generating >1019 sequences. They are selected during thymopoiesis, which releases a repertoire of about 108 unique TCRs per individual. How evolution shaped a process that produces TCRs that can effectively handle a countless and evolving set of infectious agents is a central question of immunology. The paradigm is that a diverse enough repertoire of TCRs should always provide a proper, though rare, specificity for any given need. Expansion of such rare T cells would provide enough fighters for an effective immune response and enough antigen-experienced cells for memory. We show here that human thymopoiesis releases a large population of clustered CD8+ T cells harboring α/β paired TCRs that (i) have high generation probabilities and (ii) a preferential usage of some V and J genes, (iii) which CDR3 are shared between individuals, and (iv) can each bind and be activated by multiple unrelated viral peptides, notably from EBV, CMV, and influenza. These polyspecific T cells may represent a first line of defense that is mobilized in response to infections before a more specific response subsequently ensures viral elimination. Our results support an evolutionary selection of polyspecific α/β TCRs for broad antiviral responses and heterologous immunity.
Model-based whole-brain perturbational landscape of neurodegenerative diseases
Authors: Sanz Perl Yonatan , Fittipaldi Sol , Gonzalez Campo Cecilia , Moguilner Sebastián , Cruzat Josephine , Fraile-Vazquez Matias E , Herzog Rubén , Kringelbach Morten L , Deco Gustavo , Prado Pavel , Ibanez Agustin , Tagliazucchi Enzo
Published: March 2023

The treatment of neurodegenerative diseases is hindered by lack of interventions capable of steering multimodal whole-brain dynamics towards patterns indicative of preserved brain health. To address this problem, we combined deep learning with a model capable of reproducing whole-brain functional connectivity in patients diagnosed with Alzheimer’s disease (AD) and behavioral variant frontotemporal dementia (bvFTD). These models included disease-specific atrophy maps as priors to modulate local parameters, revealing increased stability of hippocampal and insular dynamics as signatures of brain atrophy in AD and bvFTD, respectively. Using variational autoencoders, we visualized different pathologies and their severity as the evolution of trajectories in a low-dimensional latent space. Finally, we perturbed the model to reveal key AD- and bvFTD-specific regions to induce transitions from pathological to healthy brain states. Overall, we obtained novel insights on disease progression and control by means of external stimulation, while identifying dynamical mechanisms that underlie functional alterations in neurodegeneration.
Beyond laughter and smiles
Authors: Ramdas Bageshwar Bageshree , Zafar Shahila
Published: March 2023

Amid the deluge of serious social media posts regarding the COVID-19 pandemic, humorous posts brought users much-needed respite. This article reviews studies on social media-based COVID-19 humour in 42 research articles that were selected from four databases, viz. Science Direct, Scopus, Taylor & Francis, and Web of Science. After the classification and analysis of the articles on the basis of some key features, a detailed description and discussion of the findings have been carried out. The results concerning the characteristics and functions of COVID-19 humour reveal that most studies investigated image-text memes; the most important feature found was ‘humour,’ in addition to others like sarcasm, irony, satire, criticism, juxtaposition, and locality. Intertextuality played a significant role in the structure of humorous posts, especially those related to specific countries. Additionally, it shows that although research on COVID-19 humour on social media is still in an early phase, several findings appear stable across various studies included in this review. Moreover, most humour studied is not only about the virus or the disease itself, but also focuses on absurd situations individuals found themselves in due to the pandemic and the lockdown that followed.
The gender-job satisfaction paradox: the evidence of Serbia
Authors: Dašić Miloš , Mihajlov Nenad , Mihajlov Snežana
Published: March 2023

Research Question: This study investigates gender differences in job satisfaction among employees in Serbia. Motivation: The main goal of the research is examine and providing evidence the existence and scope of the paradox of gender job satisfaction. In his paper, Clark (1997)proves that women have greater job satisfaction than men. The author suggests that, in general, the higher satisfaction of women at work may be a consequence of lower job expectations as a result of the worse position in the labor market that women have had in the past. Idea:The starting point of this research is the assumption that employed women are on average more satisfied than men, despite the inferior position they occupy in the labor market. Data:The research was conducted among 468 employees in six privately owned IT and publishing companies and one state-owned company (The Pension and Disability Insurance Fund of the Republic of Serbia).The structured questionnaire was used and distributed during January 2021. Tools: The questionnaire has two parts. The first part pertains to the respondents’ demographic information such as gender, age, level of education, the sectoral structure of the company in which they are employed, management positions and years of work experience. The second part of the questionnaire referred to questions related to job satisfaction, ie it contained 8 questions in accordance with the Job Satisfaction Questionnaire(Clark, 1997), which measured the degree of satisfaction with aspects of job including general satisfaction with current job. Findings: The results research show the women are more dissatisfied with their job compared to men, despite the fact that the distinction in job satisfaction between women and men is statistically insignificant. Finding that women on the average more dissatisfaction with their jobs than man appears to be contradictory to the most of studies report that women more satisfaction with their jobs than men. Accordingly, the idea of the gender-job satisfaction paradox in conditions of high levels of gender inequality that characterizes the labor market in Serbia cannot be confirmed and accepted as a universal phenomenon.Contribution: The paper adds existing knowledge about the job-gender paradox. Evidence that there are no differences in job satisfaction between female and male employees suggests that gender discrepancies is becoming less significant.
R-package LNIRT for joint modeling of response accuracy and times
Authors: Fox Jean-Paul , Klotzke Konrad , Simsek Ahmet Salih
Published: March 2023

In computer-based testing it has become standard to collect response accuracy (RA) and response times (RTs) for each test item. IRT models are used to measure a latent variable (e.g., ability, intelligence) using the RA observations. The information in the RTs can help to improve routine operations in (educational) testing, and provide information about speed of working. In modern applications, the joint models are needed to integrate RT information in a test analysis. The R-package LNIRT supports fitting joint models through a user-friendly setup which only requires specifying RA, RT data, and the total number of Gibbs sampling iterations. More detailed specifications of the analysis are optional. The main results can be reported through the summary functions, but output can also be analysed with Markov chain Monte Carlo (MCMC) output tools (i.e., coda, mcmcse). The main functionality of the LNIRT package is illustrated with two real data applications.
Prevalence of Musculoskeletal Pain among Sonographers in Makkah Province and Factors Associated with the Pain: A Cross-sectional Study
Authors: Kanbayti Ibrahem Hussain , Awad Ibrahem Abbas , Ibrahim Rawan A , Sharif Reem H Al- , Sulbi Roaa M Al- , Almaimoni Yousef Hamoud
Published: March 2023

Introduction: Work-related musculoskeletal pain is a serious public health issue affecting healthcare providers, particularly, sonographers. The lack of research into this issue, together with the limited knowledge of factors associated with pain among Saudi sonographers promoted the authors to perform this study. Aim: To explore the prevalence of work-related musculoskeletal pain and potential factors related to this disorder among sonographers. Materials and Methods: This cross-sectional study targeted 102 sonographers working in the Radiology Departments of hospitals located in the Makkah province from September 2019 to February 2020. The questionnaire comprised 27 questions11 questions related to demographic and psychosocial, nine on work scheduling and task factors (average time per scan and amount of job tasks), one on anatomical areas affected by pain over the last six months, six questions on work-related posture factors (position of the body during scanning). Bivariate analysis was considered to investigate the relationships between workrelated musculoskeletal pain and potential factors affecting the musculoskeletal system of sonographers. Results: The prevalence of work-related musculoskeletal pain among Saudi sonographers was 81 (98.78%), and the pain was located at a single or multiple body sites, with the highest being in shoulders (70, 86.4%), followed by lower back (61, 75.3%), hand and wrist (58, 71.6%). Mental stress was only associated with shoulder pain (p-value: 0.03), and demographic factors were related to lower back, hand and, wrist pain (p-value ≤0.003). Upper back pain was significantly related to workrelated posture factors (p-value ≤0.008), and both work related posture factors, as well as task factors, have shown a significant relationship with lower back pain (p-value ≤0.04). Conclusion: Work-related musculoskeletal pain is highly prevalent among Saudi sonographers and the pain from different anatomical parts were found to be associated with different factors including psychological, demographic, task, and work-related posture factors.
A Review of Rapid Generation Advancement (RGA) in Crop Improvement
Authors: Bhargava Kotte , Abhishek E. , Madhusudhan Barla , Naveen A. , Akhil V. Sai , Yadav T. Venu , Mudhale Abhijeet , Kumar G. Anil
Published: March 2023

The use of the speed breeding method is widely considered to be the wave of the future in plant breeding. The term "speed breeding" is used to describe a rapid generational advancement technique that is used to minimise the time it takes from seed to seed, therefore reducing the length of a crop plant's typical life cycle. Plants that are not sensitive to light may have as many as six generations in a single year using this method, whereas other plants can only expect two or three generations every year. With this technique, the photoperiodic and temperature needs of crops produced in controlled-poly homes may be altered. This methodology, when combined with other cutting-edge tools like genome editing and high-throughput genotyping systems, may help breed new kinds of crops at a much quicker pace. Spacefaring food producers: NASA first conceived of this notion. Breeder's equation may be used to determine whether speed breeding is applicable to a certain crop. Light, photoperiodic regime, temperature, and humidity modification make up the backbone of the fast-breeding formula. Accelerated breeding, expedited genomic selection, improved transgenic and CRISPR-Cas9 pipelines, and the investigation of critically important agricultural plant physiological properties are just some of the numerous uses for this approach.
Modulation of the oxygen affinity of cobalt‐porphyrin by globin
Authors: Marden Michael C. , Kiger Laurent , Poyart Claude , Rashid Aftab K. , Kister Jean , Stetzkowski-Marden Françoise , Caron Genevieve , Haque Masoodul , Moens Luc
Published: July 2002

We have combined two extreme effects which influence the oxygen affinity to obtain a cobalt‐based oxygen carrier with an affinity similar to that of human adult hemoglobin (HbA). The goal was to obtain an oxygen transporter with a lower oxidation rate. Exchange of the heme group (Fe‐protoporphyrin IX) in Hb with a cobalt‐porphyrin leads to a reduction in oxygen affinity by over a factor of 10, an oxygen affinity too low for use as a blood substitute. At the other extreme, certain globin sequences are known to provide a very high oxygen affinity; for example, Hb Ascaris displays an oxygen affinity 1000 times higher than HbA. We demonstrate here that these opposing effects can be additive, yielding an oxygen affinity similar to that of HbA, but with oxygen binding to a cobalt atom. We have tested the effect of substitution of cobalt‐porphyrin for heme in normal HbA, sperm whale (SW) Mb (Mb), and high affinity globins for leghemoglobin, two trematode Hbs: Paramphistomum epiclitum (Pe) and Gastrothylax crumenifer (Gc). As for HbA or SW Mb, the transition from heme to cobalt‐porphyrin in the trematode Hbs leads to a large decrease in the oxygen affinity, with oxygen partial pressures for half saturation (P
50) of 5 and 25 mm Hg at 37°C for cobalt‐Pe and cobalt‐Gc, respectively. A critical parameter for Hb‐based blood substitutes is the autoxidation rate; while both metals oxidize to an inactive state, we observed a decrease in the oxidation rate of over an order of magnitude for cobalt versus iron, for similar oxygen affinities. The time constants for autoxidation at 37°C were 250 and 100 h for Pe and Gc, respectively.
Long‐term replication of Epstein‐Barr virus‐derived episomal vectors in the rodent cells
Authors: Mizuguchi Hiroyuki , Hosono Tetsuji , Hayakawa Takao
Published: July 2002

Plasmids containing the origin of replication, oriP, of the Epstein‐Barr virus (EBV) and EBV nuclear antigen‐1 genes replicate extrachromosomally in primate cells. However, these plasmids have been believed not to replicate in rodent cells. We demonstrate here that these plasmids can replicate in some types of rodent cells over a long period. This result should offer not only the new insight into the mechanisms of species‐specific replication of EBV, but also the possibility that an EBV‐based vector can be used for gene transfer experiments in non‐primate cells and an animal experiment regarding human gene therapy.
The compositional organization and the expression of the Arabidopsis genome
Authors: Carels Nicolas , Bernardi Giorgio
Published: July 2002

The base composition patterns of genes, coding sequences and gene expression levels were analyzed in the available long sequences (contigs) of Arabidopsis. Chromosome 5 was analyzed in detail and all chromosomes for which sequence data are now available show essentially the same large‐scale compositional properties. Guanine+cytosine levels of genes and of their coding regions, as well as gene densities and expression levels, all show a marked tendency to be higher in the distal regions of Arabidopsis chromosomes.
Novel splice variants of amphiphysin I are expressed in retina1
Authors: Terada Yoshiko , Tsutsui Ken , Sano Kuniaki , Hosoya Osamu , Ohtsuki Hiroshi , Tokunaga Akira , Tsutsui Kimiko
Published: July 2002

Using RT‐PCR‐based cDNA cloning, we identified novel splice variants of amphiphysin I, termed amph Ir, that are expressed specifically in retina. In comparison with the prototype amphiphysin I, amph Ir contained two novel insertions (inserts A and B) and one deletion. Insert A is only 9 bp in length but appears to be a determinant for the retina‐specific expression. In contrast, insert B is a large domain of 1740 bp and two shorter transcripts with 3′‐truncated insert B were also expressed. All the insert sequences were present as unidentified exons in the amphiphysin I gene on human chromosome 7. Western blot analysis of various rat tissues with anti‐insert B antibody confirmed the presence and tissue specificity of the variant proteins.
Effects of FIS Overexpression on Cell Growth, rRNA Synthesis, and Ribosome Content in Escherichiacoli
Authors: Richins Richard , Chen Wilfred
Published: July 2002

The Escherichia coli DNA binding protein FIS is a transcriptional modulator involved in the regulation of many cellular processes, including the activation of rRNA synthesis. High‐level overproduction of FIS in early, mid, or late log cultures resulted in growth‐phase‐ and media‐specific variations in cell growth, rRNA synthesis, and ribosome content. FIS overproduction caused a pronounced increase in rRNA synthesis for late‐exponential cultures but a substantial reduction in cell growth and ribosome content. The addition of simple sugars such as glucose or fructose reversed these phenomena, consistent with the functional role of FIS in carbon metabolism.
Prevalence of usual‐corrected distance visual acuity impairment in Hispanic and non‐Hispanic children and adolescents
Authors: Lee D.L. , Gómez‐Marín O. , Lam B.L. , Ma F. , Vilar N.F.
Published: July 2002

Data from the Hispanic Health and Nutrition Examination Survey and the National Health and Nutrition Examination Survey I were analysed to determine the prevalence of visual acuity impairment among US Hispanics and non‐Hispanics aged 6–19 years. The prevalence of 20/30 or worse distance visual acuity with usual or habitual correction ranged from 10.8% in non‐Hispanic whites to 19.1% in Puerto Ricans. Puerto Rican boys aged 13–19 years had significantly greater rates of moderate or greater impairment (20/70 or worse) than 6–12‐year‐old Puerto Rican boys (5.7% vs. 0.7%). The prevalence of visual impairment was generally greater in girls than in boys. Assessment and comparison of refractive error and eye disease prevalence rates are necessary in future studies to determine factors influencing prevalence of visual acuity impairment in children.
Homologous serum‐stimulated fibronectin synthesis in human retinal pigmented epithelial cells
Authors: Stocks S Z , Shiels I A , Taylor S M
Published: July 2002

Purpose: Fibronectin expression has been recorded in subretinal membranes from patients with proliferative vitreoretinopathy (PVR). Retinal pigmented epithelial (RPE) cells are a major cellular component of PVR membranes and synthesize fibronectin. We investigated the effects of human serum (as a model of vascular leakage in vivo) on the expression of fibronectin by cultured human RPE cells and compared the responses to those stimulated by fetal bovine serum (FBS).

Methods: Human RPE cells were incubated in M199 with 1, 10 and 40% human adult serum or FBS for 72 h.

Results: Retinal pigmented epithelial cells expressed maximum extracellular matrix fibronectin when exposed to 40% human serum using immunohistochemistry. Using ELISA to quantify fibronectin, 10 and 40% human serum significantly increased the total fibronectin (P < 0.01; n = 4), whereas FBS did not affect fibronectin expression.

Conclusions: The results show that human serum contains substances stimulating fibronectin synthesis in human RPE cells.
Establishment and redistribution of Longitarsus flavicornis (Stephens) (Coleoptera: Chrysomelidae) for the biological control of ragwort (Senecio jacobaea L.) in Tasmania
Authors: Ireson Je , Leighton Sm , Holloway Rj , Chatterton Ws
Published: July 2002

Ragwort flea beetle, Longitarsus flavicornis (Stephens), was first released as a biological control agent for ragwort in Tasmania in 1979. Field surveys to the end of February 1999 showed that it is now dispersed over all land known to be infested by ragwort in southern Tasmania, and over about 90% of the major infestations in the north. A redistribution program has been undertaken to accelerate spread of L. flavicornis by transferring field collected adults from established field sites during summer and autumn. Since 1986, almost 2 million adults have been distributed to 879 sites, with over 80% of transfers taking place between 1993 and 1999. A minimum of 1000 adults released/site resulted in establishment at 90% of the sites. Although large (> 90%) reductions in ragwort densities have been recorded, we suspect that prevailing site conditions such as flooding and incompatible management practices such as use of boom‐sprayed herbicides, are restricting efficacy of L. flavicornis on many properties. Attempts to address this problem are now being made through use of integrated control strategies and establishment of complementary biological control agents.
Distortionless picosecond pulse amplification and gain compression in a traveling-wave InGaAsP optical amplifier
Authors: Wiesenfeld J. M. , Eisenstein G. , Tucker R. S. , Raybon G. , Hansen P. B.
Published: July 2002

Pulses of 3–9 ps duration at wavelengths between 1.22 and 1.27 μm are amplified by a 1.3 μm InGaAsP traveling-wave optical amplifier. The gain decreases linearly with the output energy by up to 2.6 dB at the highest available energies. The output energy and peak power of the amplified pulses are as large as 4 pJ and 400 mW, respectively. It is shown that the gain compression can be described by treating the amplifier as a homogeneously broadened two-level system. No distortion of the pulse shape is observed after amplification.
High-speed distributed feedback lasers grown by hydride epitaxy
Authors: Temkin H. , Logan R. A. , Karlicek R. F. , Strege K. E. , Blaha J. P. , Gabla P. M. , Savage A. , Oatis K.
Published: July 2002

We have used hydride vapor phase epitaxy to prepare re-entrant mesa buried-heterostructure distributed feedback lasers. The grating is overgrown uniformly with minimal amplitude reduction. A semi-insulating Fe-InP blocking layer around the etched mesas is grown very reproducibly with little dependence upon the details of mesa etching. Laser diodes show cw thresholds of ∼25 mA. Single-mode operation has been shown at power levels as high as 18 mW and temperatures up to 100 °C. Modulation bandwidth in excess of ∼8 GHz has been demonstrated with simple and reliable full surface Ohmic contacts.
New gain mechanism for wave amplification in photorefractive materials
Authors: Ringhofer K. H. , Solymar L.
Published: July 2002

It is shown that there is a gain mechanism in three- and four-wave forward interactions in which power is transferred inwards from the pump beams to the signal beams. The special case of amplifying a wave halfway between the pump waves is discussed.
Photovoltaic spectroscopy of InGaAs/GaAs superlattices
Authors: Hua B. Y. , Fortin E. , Roth A. P. , Masut R. A.
Published: July 2002

Photovoltaic spectra of InGaAs/GaAs multiple quantum wells grown by metalorganic vapor phase epitaxy show several well defined spectral structures which are interpreted in terms of the sample characteristics. Results obtained by this relatively simple method are comparable to data obtained by other optical techniques on the same material, and in good agreement with calculations taking into account the strain-induced splitting and the coupling between the wells.
Study on step coverage and (111) preferred orientation of aluminum film deposited by a new switching bias sputtering method
Authors: Onuki Jin , Nihei Masayasu , Suwa Motoo , Koubuchi Yasushi , Fukada Shini-chi , Miyazaki Kunio
Published: July 2002

A new switching bias sputtering method capable of improving both the step coverage at the small contact holes and the quality of aluminum film has been developed for the formation of reliable interconnection of very large scale integrated circuits. The method features alternating operation of standard and bias sputtering in 5×10−4 Torr of argon. Aluminum film deposited using this method is seen to have seven times higher (111) orientation and four times higher electromigration resistance than simple bias-sputtered aluminum film. Additionally, the step coverage is raised to 50% for a perpendicular step with 1 μm depth and 1 μm width.
Atomic-layer epitaxy of (111)CdTe on BaF2 substrates
Authors: Faschinger W. , Sitter H. , Juza P.
Published: July 2002

Atomic-layer epitaxy of (111)CdTe single crystalline films on (111)BaF2 substrates is investigated. It is shown that a set of growth parameters exists in which the average growth per cycle of opening and closing the shutters of the constituent element sources is one monolayer. In a substrate temperature range between 260 and 285 °C the growth process is self-regulative, that means, it is independent of the Te beam intensity and the substrate temperature. At substrate temperatures higher than 285 °C growth is still self-regulative, but the average growth rate per cycle is less than one monolayer.
Fabrication of n+/p InP solar cells on silicon substrates
Authors: Keavney C. J. , Vernon S. M. , Haven V. E. , Wojtczuk S. J. , Al-Jassim M. M.
Published: July 2002

InP solar cells were fabricated from films deposited by metalorganic chemical vapor deposition on Si substrates (using a GaAs buffer layer) and on GaAs substrates. Air mass zero efficiencies of 7.1% and 9.4%, respectively, were achieved. Prospects are good for improving the material quality of the InP films, but more work is needed to make the n+-p-p+ structure of the InP solar cells compatible with the silicon substrates, which cause n-type doping of the III-V films.
Diamond films for laser hardening
Authors: Albin S. , Watkins L. , Ravi K. , Yokota S.
Published: July 2002

Diamond has many unique physical properties useful as thin-film coatings for laser optics. The calculated value of the laser-induced stress resistance parameter of diamond is orders of magnitude higher than any other material and, therefore, diamond films should have a higher laser damage threshold. This is confirmed by laser damage experiments carried out on free-standing polycrystalline diamond films. Materials susceptible to laser damage can be protected by diamond thin-film coatings to enhance the damage threshold. This is demonstrated in the case of diamond coated silicon substrate.
Coherent operation of injection-locked monolithic surface-emitting diode laser arrays
Authors: Jansen M. , Yang J. J. , Heflinger L. , Ou S. S. , Sergant M. , Huang J. , Wilcox J. , Eaton L. , Simmons W.
Published: July 2002

A row of six surface-emitting GaAlAs laser diode arrays was locked in a coupled resonator configuration by means of interconnecting waveguides. An external master oscillator was injected into the first array in order to achieve single longitudinal mode operation and wavelength tunability. Spectral data show all six devices were locked in a single longitudinal mode, with tunable operation of over 60 Å. Far-field fringe visibilities greater than 60% were achieved at 100 mW output powers.
Tunable twin-guide laser: A novel laser diode with improved tuning performance
Authors: Amann M.-C. , Illek S. , Schanen C. , Thulke W.
Published: July 2002

A new wavelength tunable laser diode with a basically continuous tuning behavior is presented. This essential progress is achieved by transversely tuning the effective index of a distributed feedback laser using a twin waveguide. Due to the built-in synchronization of the Bragg wavelength and the optical cavity length, the wavelength is controlled by only a single current. The device technology and preliminary experimental results demonstrating the transverse tuning mechanism are presented.
Dependence of emission wavelength on cavity length and facet reflectivities in multiple quantum well semiconductor lasers
Authors: Wilcox J. Z. , Ou S. , Yang J. J. , Jansen M. , Peterson G. L.
Published: July 2002

The spectral emission characteristics of multiple quantum well semiconductor lasers of the Fabry–Perot type are a strong function of laser cavity length and mirror reflectivities. 15 nm theoretically predicted wavelength shifts were validated experimentally. This has immediate applications in the development of semiconductor laser-pumped solid-state lasers, where accurate control of the semiconductor laser pump spectral emission is essential.
Hole transport through minibands of a symmetrically strained GexSi1−x/Si superlattice
Authors: Park J. S. , Karunasiri R. P. G. , Wang K. L. , Rhee S. S. , Chern C. H.
Published: July 2002

The hole transport through the minibands of a GexSi1−x/Si superlattice is observed for the first time. The symmetrically strained, short-period GexSi1−x/Si supperlattice is grown on a Gex/2Si1−x/2 /Si buffer layer. The current-voltage and conductance-voltage characteristics show two peaks which are attributed to the conduction of light holes through the first and second light hole minibands. The light hole miniband energies are estimated by thermionic emission analysis and are in good agreement with the calculated values using effective mass approximation.
Thermal and ion beam induced reactions in Ni thin films on BP(100)
Authors: Kobayashi N. , Kumashiro Y. , Revesz P. , Li Jian , Mayer J. W.
Published: July 2002

Thermal and ion beam induced reactions in Ni thin films on BP(100) have been investigated. For thermally annealed samples the reaction of the Ni layer on BP started at temperatures between 350 and 400 °C and the formation of the crystalline phase corresponding to a composition of Ni4BP was observed at 450 °C. It was observed that oxygen in the Ni layer could retard the progress of the reaction. The full reaction of the Ni layer with BP induced by energetic heavy ion bombardments (600 keV Xe) was observed at 230 °C. The crystalline phase has the same composition and x-ray diffraction pattern for both thermal and ion-induced reactions.
High-field transport in semiconductors based on eigenvalue solution to Boltzmann equation
Authors: Krishnamurthy Srinivasan , Sher A. , Chen A.-B.
Published: July 2002

The Boltzmann equation is solved by expanding the distribution function in terms of a finite number of basis functions. The zero eigenvalue of the resulting matrix is solved for the hot-electron distribution. This method arrives at the solution at least two orders of magnitude faster than the commonly used Monte Carlo method. Using the scattering rates due to ionized impurities, phonons, alloy disorder, and intervalley scattering calculated from a realistic band structure, we obtain velocity-field curves for various semiconductor alloys and compounds without any adjustable parameters. The results are in good agreement with experiments.
Measurement of the fundamental modulation response of a semiconductor laser to millimeter wave frequencies by active-layer photomixing
Authors: Newkirk Michael A. , Vahala Kerry J.
Published: July 2002

The room-temperature modulation response of a GaAs/GaAlAs semiconductor laser (relaxation resonance frequency, νR=6.5 GHz) is measured to 37 GHz using the active-layer photomixing technique. The measured response function agrees with the theoretical ideal, and there is no indication of device parasitic effects. An ultrahigh-finesse Fabry–Perot interferometer is used to detect the optical modulation, which appears as sidebands in the laser field spectrum. With a moderately faster laser diode (i.e., νR∼10 GHz), the modulation response should be measurable beyond 100 GHz.
Femtosecond 1.4–1.6 μm infrared pulse generation at a high repetition rate by difference frequency generation
Authors: Kurokawa Kenji , Nakazawa Masataka
Published: July 2002

Tunable subpicosecond infrared pulses have been generated in the 1.4–1.6 μm region by mixing a 1.064 μm Nd:YAG laser pulse and a visible subpicosecond pulse from a cavity dumped, synchronously pumped dye laser. Pulses as short as 94 fs with a peak power of 8.4 kW have been obtained with a KTP crystal at a rate of 3.8 MHz.
On-line determination of alloy composition during ternary III/V molecular beam epitaxy
Authors: Tsao J. Y. , Brennan T. M. , Klem J. F. , Hammons B. E.
Published: July 2002

We describe a simple, new method for deducing surface alloy composition during ternary III/V molecular beam epitaxy. The method is based on on-line reflection mass spectrometry of the group V flux ‘‘reflected’’ from the surface during momentary terminations of individual group III fluxes.
Superconducting Bi-Sr-Ca-Cu-O crystalline fibers prepared by the micro-Czochralski method
Authors: Kurosaka Akihito , Aoyagi Mamoru , Tominaga Haruo , Fukuda Osamu , Osanai Hiroshi
Published: July 2002

Superconducting Bi-Sr-Ca-Cu-O crystalline fibers were successfully prepared by the micro-Czochralski method from Bi2Sr2 CaCu2 Ox source ceramic rods. The maximum length of the fibers obtained was 55 mm (0.3 mm diameter). The fiber crystal grains were oriented with the current carrying a-b basal planes parallel to the fiber axis. The values of Tc (zero) and Jc (77 K and zero magnetic field) for these fibers were ∼84 K and ∼3170 A/cm2 , respectively.
Generation of widely tunable intense far-infrared radiation pulses by stimulated Raman transitions in methylfluoride gas
Authors: Lang P. T. , Sessler F. , Werling U. , Renk K. F.
Published: July 2002

We report on the generation of widely tunable intense far-infrared radiation pulses by stimulated Raman transitions in methylfluoride gas. Using a tunable high-pressure CO2 laser we achieved, by P-branch tuning of stimulated Raman transitions in 12CH3F and 13CH3F gases, tunable generation of radiation in a series of intervals in the spectral range from 37 to 72 cm−1 covering 20% of this range. Possibilities of further extension of the tuning regions are also discussed.
Electron beam lithography using surface reactions with ClF3
Authors: Matsui Shinji
Published: July 2002

Direct writing onto poly(methylmethacrylate) (PMMA) resist has been demonstrated by electron beam induced surface reaction using a ClF3 gas source. The electron beam stimulated etched depth for PMMA resist is proportional to the electron dose. Etched depth profile control has been demonstrated by changing doses. A 0.5 μm linewidth pattern has been fabricated at a 2×10−3 C/cm2 dose.
Time-resolved measurement of tunneling and energy relaxation of hot electrons in GaAs/AlGaAs double quantum well structures
Authors: Sawaki N. , Höpfel R. A. , Gornik E. , Kano H.
Published: July 2002

The tunneling and cooling times of photoexcited hot electrons in AlGaAs/GaAs double (one narrow and the other wide) quantum well structures have been measured using photoluminescence excitation correlation spectroscopy. The tunneling time was of the order of 200 ps for a 60 Å barrier. The tunneling is the indirect process assisted by the emission of optical phonons. The relaxation time of electrons as a function of the kinetic energy shows a threshold for cooling via the emission of optical phonons.
Effect of Al mole fraction on electron emission at the AlxGa1−xAs/GaAs interface
Authors: Kleine J. S. , Melloch M. R. , Cooper J. A.
Published: July 2002

We report the first direct measurement of electron storage time at the AlxGa1−xAs/GaAs interface as a function of Al mole fraction x. Storage capacitors with x=0.4, 0.6, 0.8, and 1.0 were fabricated and their inversion layer electron retention times measured. The optimal mole fraction for electron retention is in the range 0.4≤x≤0.6.
Resonant tunneling through X-valley states in GaAs/AlAs/GaAs single-barrier heterostructures
Authors: Beresford R. , Luo L. F. , Wang W. I. , Mendez E. E.
Published: July 2002

Clear negative differential resistance has been observed in a GaAs/AlAs/GaAs single-barrier heterostructure due to the presence of a quasi-bound state associated with the X-point profile. This surprising result is due to the fact that although the Γ-point profile of this heterostructure is a simple single tunneling barrier, the X-point profile actually constitutes a quantum well some 0.3 eV deep lying about 0.2 eV above the Γ point of GaAs. The experimental evidence is a sharp cutoff in conductance at about 0.36 V bias, characteristic of tunneling via a confined state.
High quality long-wavelength lasers grown by atmospheric organometallic vapor phase epitaxy using tertiarybutylarsine
Authors: Miller B. I. , Young M. G. , Oron M. , Koren U. , Kisker D.
Published: July 2002

High quality long-wavelength InGaAsP/InP lasers were grown by atmospheric organometallic vapor phase epitaxy using tertiarybutylarsine (TBA) as a substitute for AsH3. Electrical and photoluminescence measurements on InGaAs and InGaAsP showed that TBA-grown material was at least as good as AsH3 material in terms of suitability for lasers. From two wafers grown by TBA, current thresholds Ith as low as 11 mA were obtained for a 2-μm-wide semi-insulating blocking planar buried heterostructure laser lasing near 1.3 μm wavelength. The differential quantum efficiencies ηD were as high as 21%/facet with a low internal loss α=21 cm−1. In addition Ith as low as 18 mA and ηD as high as 18% have been obtained for multiplequantum well lasers at 1.54 μm wavelength. These results show that TBA might be used to replace AsH3 without compromising on laser performance.
AlGaAs grating surface-emitting beam deflector utilizing carrier-induced refractive index change
Authors: Tone Kiyoshi , Nagata Hisao , Yamashita Ken
Published: July 2002

A new type of AlGaAs grating surface-emitting beam deflector is proposed. The deflection is controlled by a carrier-induced refractive index change of the waveguide on which the grating output coupler is fabricated. About 0.6° of the maximum deflection angle is obtained at the injection current of 1.6 A. This corresponds to about 12 resolvable spots.
Nonresonant absorption coefficient of single-crystal films of polydiacetylene measured by photothermal deflection spectroscopy
Authors: Thakur M. , Frye R. C. , Greene B. I.
Published: July 2002

Using photothermal deflection spectroscopy we have measured the nonresonant absorption coefficient of poly (bis-p-toluene sulfonate) of 2,4 hexadiyne-1,6 diol (PTS) single-crystal films for the first time. The absorption coefficient continuously decreases from the reported peak value of ∼9×105 cm−1 at 620 nm (exciton band) to ∼100 cm−1 at 700 nm and finally reaches a value of ∼0.30 cm−1 at λ∼1.3 μm for polarization parallel to the chain axis. Above λ∼1050 nm, the absorption coefficient becomes polarization independent. The low nonresonant absorption coefficient as measured is desirable in terms of nonlinear optical device applications of this material.
GaAs/AlGaAs single-mode optical waveguides with low propagation loss and strong optical confinement
Authors: Seto M. , Shahar A. , Deri R. J. , Tomlinson W. J. , Yi-Yan A.
Published: July 2002

Singe-mode optical waveguides have been fabricated with a saturated bromine water etchant using single-heterostructure GaAs/AlGaAs epitaxial material, with propagation losses as low as 0.6 dB/cm for 1.66 μm deeply etched ribs (Δneff≂2.4) and losses below 0.2 dB/cm for 0.23 μm shallowly etched ribs (Δneff =0.0067), measured at λ=1.5 μm.
Ultrafast modulation with subpicosecond recovery time in a GaAs/AlGaAs nonlinear directional coupler
Authors: Jin R. , Sokoloff J. P. , Harten P. A. , Chuang C. L. , Lee S. G. , Warren M. , Gibbs H. M. , Peyghambarian N. , Polky J. N. , Pubanz G. A.
Published: July 2002

All-optical modulation is observed at room temperature in a GaAs/AlGaAs multiple quantum well nonlinear directional coupler using femtosecond pulses. The origin of the ultrafast (<500 fs) recovery of the device is attributed to the optical Stark effect.
Impurity-induced disordering in fractional-layer growth on a (001) vicinal surface by metalorganic chemical vapor deposition
Authors: Saito H. , Fukui T.
Published: July 2002

(AlAs)1/2(GaAs)1/2 fractional-layer superlattices (FLSs) are grown on a (001) GaAs substrate, tilted slightly in the [1̄10] direction using metalorganic chemical vapor deposition. The periodic structures are analyzed by x-ray superlattice satellite diffraction. The results suggest that the step flow mode from monolayer step is a dominant crystal growth process. However, the satellite intensities drastically decrease under heavy Si impurity doping conditions (n>2×1017 cm−3), showing that impurity-induced disordering occurs during fractional-layer growth. The growth mechanism under impurity doping conditions is also discussed.
All-optical tuning of waveguide nonlinear distributed feedback gratings
Authors: Ehrlich J. E. , Assanto G. , Stegeman G. I.
Published: July 2002

The nonlinear properties of a distributed feedback grating in a waveguide characterized by a diffusive thermal nonlinearity were investigated experimentally. Reflection and transmission were measured in an InSb planar structure, and all-optical tuning of the reflectivity was achieved either by a guided wave incident onto the distributed feedback grating near its Bragg condition, or by a second guided beam tuned far from the Bragg condition.
Raman study of de-relaxation and defects in amorphous silicon induced by MeV ion beams
Authors: Roorda S. , Poate J. M. , Jacobson D. C. , Dennis B. S. , Dierker S. , Sinke W. C.
Published: July 2002

Raman spectroscopy is used as a probe of the state of amorphous Si (a-Si) and damaged crystalline Si. MeV ion beams have been used to irradiate structurally relaxed a-Si. When the density of Si atoms displaced by nuclear collisions exceeds 5%, the a-Si is ‘‘de-relaxed’’, and thus returns to its as-implanted state. This behavior is an indication that point defect complexes exist in a-Si and play an important role in the process of structural relaxation.
Hydrogen beam stimulated low-temperature dissociation of organometallics—application for lowering the growth temperature in a metalorganic chemical vapor deposition process
Authors: Jagannathan G. V. , Andrews Merrill L. , Habig Alec T.
Published: July 2002

A hydrogen atomic beam generated by microwave discharge was successfully used for dissociating trimethylaluminum (TMA) at the low substrate temperature of 300 °C. The results indicate that ‘‘H’’ atomic beam can stimulate the clean and complete dissociation of organometallics at substrate temperatures only slightly above the onset of thermal pyrolysis of the organometallics. The clean dissociation of TMA is dependent on both thermal as well as plasma stimulation. Residual oxygen present in our system resulted in growth of high quality Al2O3 films. In a clean metalorganic chemical vapor deposition system H atomic beam can be used to dissociate organometallics at significantly lower temperatures (300–400 °C) relative to the presently used growth temperature of 700 °C.
Trapped positive charge in plasma-enhanced chemical vapor deposited silicon dioxide films
Authors: Buchanan D. A. , Stathis J. H. , Wagner P. R.
Published: July 2002

We report an investigation of trapped positive charge in as-fabricated plasma-enhanced chemical vapor deposited SiO2 films using electrical and spin resonance techniques. We show that the positive charge results from donor-like ‘‘slow’’ interface states (‘‘anomalous positive charge’’) rather than trapped holes, and that most (∼95%) of the positive charge is not related to E′ centers. The positive charge is similar to that seen in electron-injected thermally grown SiO2, and unlike radiation-induced trapped holes.
Optimization of modulation ratio and insertion loss in reflective electroabsorption modulators
Authors: Pezeshki B. , Thomas D. , Harris J. S.
Published: July 2002

We show theoretically that the maximum modulation ratio in Fabry–Perot reflective electroabsorption modulators for a given insertion loss is solely a function of the ratio of the maximum to minimum absorption. We increase this ratio by using thinner quantum wells than are conventionally used and obtain significantly improved performance. We obtain an insertion loss of 1.2 dB and a modulation ratio of 7.5 with a 5 V operating bias.
Bias stress-induced instabilities in amorphous silicon nitride/hydrogenated amorphous silicon structures: Is the ‘‘carrier-induced defect creation’’ model correct?
Authors: Gelatos A. V. , Kanicki J.
Published: July 2002

The effects of positive and negative bias stress on hydrogenated amorphous silicon nitride/hydrogenated amorphous silicon (a-SiNx:H/a-Si:H) structures are investigated as a function of stress time, and stress temperature. It is shown that bias stress induces a parallel shift of the capacitance voltage (C-V) characteristics. The direction of the C-V shift depends on the sign of the applied stress voltage, while the magnitude of the C-V shift depends on stress time and temperature in a manner which is identical to that observed in a-Si:H thin-film transistors. In addition, it is shown that positive bias stress increases the number of localized states in the a-Si:H mobility gap, but negative bias stress does not. However, the observed increase cannot account for the corresponding C-V shift. These results lead us to conclude that the C-V shift is not induced by dangling bond defects in a-Si:H but rather by carrier trapping in the insulator.
Transport properties of InxGa1−xAs/GaAs strained quantum well delta-doped heterostructures grown by molecular beam epitaxy
Authors: Hong W.-P. , Zrenner A. , Kim O. H. , DeRosa F. , Harbison J. , Florez L. T.
Published: July 2002

We have investigated the transport properties of two-dimensional electron systems in strained InxGa1−xAs channels confined in a potential well formed by delta doping and GaAs barriers. The dependence of the transport parameters on the indium composition has been studied using Hall, Shubnikov–de Haas, and cyclotron resonance measurements. Experimental measurements of the effective mass have been compared with theoretical data obtained from self-consistent calculations, which take account of effects due to biaxial strain and nonparabolicity on the band structure of InxGa1−xAs.
Ultrafast coplanar air-transmission lines
Authors: Dykaar D. R. , Levi A. F. J. , Anzlowar M.
Published: July 2002

We demonstrate subpicosecond electrical pulse propagation using coplanar air-transmission lines. Rise times of 0.8 ps after 2.8 mm of propagation are achieved with a velocity of propagation which is 86% of the speed of light in vacuum. Our results suggest that intrachip communication in digital circuits with rise times as short as 1 ps is readily achievable using electrical signals.
Dynamic and static response of multielectrode lasers
Authors: O’Gorman J. , Levi A. F. J. , Nottenburg R. N. , Tanbun-Ek T. , Logan R. A.
Published: July 2002

We compare the measured and calculated light output of a semiconductor laser modulated by a saturable intracavity absorber. An accurate description of the dynamic and static behavior requires inclusion of both a carrier concentration dependent recombination rate and a voltage-dependent saturable absorption.
Sweeping photoreflectance spectroscopy of semiconductors
Authors: Shen H. , Dutta M.
Published: July 2002

We report a new type of photoreflectance (PR) by means of sweeping the pump laser beam. The modulation is achieved by moving the position of the pump beam with respect to the probe beam. In the conventional photoreflectance (using a mechanical chopper) the problem is caused by photoluminescence (PL) produced by the pump light. This is particularly acute at low temperatures where the PL is large. In our novel sweeping photoreflectance (SPR) technique the pump intensity is constant. Hence the problem associated with the luminescence is eliminated. Therefore SPR spectra can be obtained at much lower temperatures than conventional PR. The signal to noise ratio in SPR is usually better than that in conventional PR. The sources of noise in both conventional and sweeping photoreflectance is also discussed.