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We investigated the near‐band‐edge photoluminescence from semi‐insulating GaAs crystals after they were annealed either in the wafer form or in the bulk form. Our results, with respect to the uniformity achieved after annealing, are in agreement with previous studies. The 1.360‐eV emission band which is seen in annealed crystals and which has been taken to imply a VAs related rapid diffusion process as the mechanism responsible for the annealing‐induced uniformity, is shown not to be connected with it. We also cite evidence which questions the involvement of VAs in the band. From data in the literature we estimate the diffusion coefficient of VAs and find it to be too low to bring about bulk equilibrium and uniformity via vacancy diffusion from the surface at the annealing temperatures. We conclude that the local rearrangement of defects is a viable mechanism for producing uniformity during post‐growth annealing.

A commercially viable GaAs device technology for field-effect transistors, integrated circuits, and lasers is critically dependent on the availability of high-quality, single-crystal boules with controlled diameter. We have modeled a diameter control scheme based on the monitoring of crystal weight for liquid-encapsulated Czochralski (LEC) growth of GaAs. The presence of the B 2 O 3 liquid encapsulant and significant capillary forces make the direct interpretation of the weight-gain signal and its time derivative (DWGS) more complicated in comparison with pulled materials such as oxide crystals. We have formulated a realistic model for the LEC growth of axisymmetric crystals and have derived the differential equation relating the time evolution of the DWGS to radius and length. We show that the magnitude of the DWGS at the crystal's “shoulder” is inversely related to the radius of curvature. Furthermore, the meniscus by itself gives rise to a precursor or early warning in the signal, which means that the maximum in DWGS precedes the maximum in shape by a few hundred seconds. The existence of a secondary maximum or aftershock in the signal that is the sole consequence of liquid encapsulation is also demonstrated. Excellent agreement has been obtained between DWGS and the signal predicted from the measured shape of a grown crystal. Thus, prospects for automatic diameter control are encouraging.

GaP (Zn, O) crystals pulled from nonstoichiometric melts by the liquid‐encapsulation Czochralski (LEC) technique bridge the gap between the red photoluminescent quantum efficiencies of platelets grown from solution and crystals pulled by LEC from a stoichiometric melt. A linear correlation is shown to exist between the nonradiative shunt‐path component of the total reciprocal minority‐carrier lifetime and the Ga‐vacancy concentration of these different crystals.

SummaryThirteen- to sixteen-day mouse embryos (Witschi stages 30–34) were tested for whole blood coagulation and prothrombin times. Both times were found to be significantly longer in the embryos than in the adults, the times decreasing with embryonic development. The significance of these resluts was discussed in terms of reported research on other animals.

A technique for determining relative minority‐carrier lifetimes and relative Zn–O center concentrations in GaP (Zn, O) is presented. This method utilizes relative steady‐state measurements of above‐ and below‐gap excited red luminescence. The technique is applied to a series of GaP (Zn, O) crystals and the relative lifetime measurements are correlated with absolute measurements obtained by a different method. Minority‐carrier lifetimes varying from 0.5 to 25 nsec were measured.

A study of the luminescence and doping characteristics of liquid encapsulation Czochralski (LEC) grown GaP(Zn, O) is presented. Sections from the seed, middle and tail regions of 8 crystals grown from melts containing varying amounts of gallium oxide and zinc were examined with respect to red photoluminescence quantum efficiency, minority carrier lifetime, hole concentration and concentration of paired and unpaired oxygen. The measured minority carrier lifetimes in these crystals were found to be 2–3 orders of magnitude shorter than in crystals grown from solution with comparable zinc and oxygen incorporation. This result indicates that a strong shunt path for electron recombination exists in the LEC crystals, which in turn accounts for their lower red photoluminescence efficiency when compared with the efficiency of solution grown crystals.

The stability of the electrical and structural properties of GaAs directly deposited on Si by metalorganic chemical vapor deposition is examined. Extended annealing at 900 °C leads to substantial diffusion of Si across the heterointerface while under the same conditions there is no significant motion of Si incorporated as a dopant into the GaAs surface region. The degree of enhancement of Si diffusion ranges from a factor of ∼250 for 0.5‐μm‐thick GaAs films to ∼5 for 4‐μm‐thick films. The annealing time and GaAs layer thickness dependence of Si diffusivity near the interface is consistent with a defect‐modulated mechanism. A large fraction of this mobile Si is electrically inactive.

Rapid thermal annealing of GaAs within an enclosed, SiC‐coated graphite susceptor is shown to eliminate slip formation during implant activation treatments (900 °C, 10 s) and to provide much better protection against surface degradation at the edges of wafers compared to the more conventional proximity method. The peak carrier concentration obtained in Si‐implanted (3×1012 cm−2, 60 keV) GaAs by both methods is comparable, but the wafers annealed in the susceptor have tighter carrier profile width distributions measured over the whole wafer area.

Recent advances in heterostructure bipolar transistor technology have created a need for p‐type doping at levels ≥1020 cm−3. Furthermore, such levels may eliminate the need for alloying during ohmic contact formation. We have achieved p‐type doping levels as high as 5×1020 cm−3 using an unconventional dopant, C, derived from the gaseous source chemical, trimethylgallium (TMG), during metalorganic molecular beam epitaxial (MOMBE) growth of GaAs. We have controllably achieved doping levels between 1019 and 5×1020 cm−3 by diluting the TMG flow with another metalorganic, triethylgallium (TEG). By utilizing the so‐called δ‐doping or atomic planar doping method we have also been able to grow C‐doped spikes with hole concentrations as high as 7×1019 cm−3, with a full width at half maximum of ∼50 A at 300 K. This doping level is the highest yet reported for planar doping, and the narrow width indicates that the C atoms are restricted to one or two atomic planes. By switching out the TMG, and switching in the TEG ...

Miyazawa et al. [Appl. Phys. Lett. 43, 853 (1983)] have recently established a spatial correlation between variations in field‐effect transistor performance and nonuniformities in the cathodoluminescence (CL) efficiency of semi‐insulating (SI) GaAs substrates. In this study, we compare the CL uniformity of both Cr‐doped and undoped SI GaAs crystals grown by the liquid‐encapsulated Czochralski (LEC) technique with undoped SI crystals grown by the horizontal gradient freeze (HGF) technique. In contrast to the LEC crystals, HGF GaAs has extremely uniform CL characteristics which should result in uniform device performance.

A dramatic dependence on crystal stoichiometry has been observed for the donor activation efficiency of low doses of Si ions implanted into undoped semi‐insulating GaAs. Samples from liquid encapsulated Czochralski crystals grown from melts containing As concentrations varying from 47 1/2 to 65 at. % were implanted with 100 keV 29Si ions at a dose of 5×1012 cm−2. Following a rapid, capless annealing cycle (950 °C, 5 s), the surface‐depletion corrected activation efficiency ranged from 26 to 91%, with the higher efficiencies for higher As concentrations. In contrast, co‐implantation of As and Si into standard (50 at. % As) GaAs resulted in an increase in activation efficiency from 59 to 68% for optimum As doses.

Measurements of anisotropy in implanted bubble films indicate that in addition to straining the lattice, implantation also has the effect of suppressing the growth‐induced anisotropy. After annealing at 1000 °C, most of the as‐grown anisotropy is restored, which points to oxygen defects as the most likely mechanism for the effect. The Curie temperature has been found to be lowered by as much as 70 °C by implantation at a typical device dose, and the anisotropy of the implanted layer varies quite rapidly with temperature at elevated temperatures. The results indicate that with proper choice of material parameters and implantation conditions safisfactory bubble propagation can be obtained in high density small bubble diameter devices based on ion‐implanted propagation patterns over a wide temperature range.

Epitaxial GaAs layers were grown by metalorganic chemical vapor deposition on Si‐on‐insulator structures formed by high dose oxygen implantation. The quality of the GaAs films was examined as a function of layer thickness (0.01–4 μm). The surface morphology, ion backscattering yield, x‐ray diffraction peak width, and Si implant activation efficiency all improve substantially with GaAs thickness. At a film thickness of 4 μm many of these properties are comparable to bulk GaAs, but some cracking of the epitaxial film is evident. Cross‐sectional transmission electron microscopy reveals an average defect density of ∼108 cm−2 in the GaAs layer, which is similar to the density in GaAs films grown directly on Si.

Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above ~ 6x10^{19} electron volts and the positions of active galactic nuclei (AGN) lying within ~ 75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. AGN or objects having a similar spatial distribution are possible sources., Comment: 22 pages, 2 figures

We have recently been investigating a chemical phenomena which we believe can be made the basis of a very simple thermal imaging device. The proposed device is based on the temperature sensitivity of the light output of an appropriatechemiluminescent system. Theoretical considerations and some preliminary results are presented below.

Necrotizing enteritis is a clinico-pathological entity, marked by segmentary necrosis of jejunum and ileum, variously extended, and is a rather rare picture, the etiopathogenesis of which is prevailingly supported by troubles in the intestinal circulation or by intestinal locations of reactions of hypersensitivity (Arthus-similar allergic reaction). The authors start from a case they had the opportunity to observe and successfully surgically treated, and discuss its etiopathogenetic and therapeutical implications in the light of an up-to-date reviewing of the literature thereabout.

College undergraduates were asked the degree to which they believed certain behaviors and characteristics are present in mentally retarded and mentally ill persons. Comparisons of responses showed that subjects clearly differentiated the concepts, although several areas overlapped. Mental retardation was characterized by physical stigmata and brain damage, developmental delays, and cognitive deficits; mental illness, by emotional lability due to environmental, hereditary, or mixed factors. How knowledge of people's perceptions of these disorders is essential for a more complete understanding of reactions to group homes, mainstreaming, and other "normalized" placements was discussed.

Vertebral hydatidosis is a rare localization of echinococcosis. In fact, its incidence is less than 1% of the cases in the literature. The authors report a personal observation and describe main features of the disease.

The Ga concentration in crystals prepared by a variety of techniques (pulled by the liquid encapsulation Czochralski technique from stoichiometric or nonstoichiometric melts, solution grown, and annealed) has been determined by precision coulometric titration, yielding the experimental solidus boundary which exhibits an excess of Ga along the Ga‐rich liquidus. Based on a thermodynamic model, assuming that neutral Ga and P vacancies are the predominant native defects, the analysis of the solidus data permitted the evaluation of the vacancy concentrations over a wide temperature range. At the melting point of (1465°C) there are 8 × 1018 and 1.3 × 1019 cm−3 Ga and P vacancies, respectively, in the crystal. The calculated solidus curve well represents the totality of experimental data and shows retrograde temperatures at 1375° and 1400°C on the Ga‐ and P‐rich sides, respectively. The enthalpies and entropies associated with vacancy formation are given and discussed. It is shown that the data provide strong additional support to the previous identification of Ga vacancies with killer centers in .

480 cases of advanced gastric carcinoma are classified according to Laurén or WHO and correlated to age and sex of the patients. The modal value of the incidence for age of the mucinous histologic type is 61-65 years for the men and 71-75 years for the women, while in the signet ring cell histologic type is 50 years in both sexes. These relationship, obtained only by the WHO classification, suggest that mucinous and signet ring cell type constitute distinct histoepidemiological entities.

The results of a low temperature (5K) photoluminescence study of hydrogenation of GaAs on InP grown by metal organic chemical vapor deposition are presented. An emission band at ~ 1.4 eV originating from the GaAs/InP interracial region shows a 30 fold increase in intensity relative to the GaAs band edge emission after exposure to hydrogen plasma for 30 min at 250°C. This improvement in intensity is attributed to hydrogen passivation of defects at the heterointerface caused by the large (≈4%) lattice mismatch between GaAs and InP. The passivation effect recovers on annealing the hydrogenated sample at 350°C. Excitation dependence of the ~1.4 eV band suggests that the interfacial region consists of a compositionally graded layer. Further, this band shifts to higher energy on annealing the sample in the temperature range 150-450°C with the hydrogenated sample exhibiting a larger shift than the untreated sample. It is suggested that the annealing induced peak shift arises due to intermixing of the compositionally graded interface and that the degree of intermixing is greater in the hydrogenated sample compared to the untreated sample.

Stimulus encoding was studied with a group of mentally retarded and nonretarded adults. Two sets of 24 nonverbal stimuli were selected; one had a wide range of stimulus structure variables and the other, a representative sample of stimuli. Performance on a match-to-sample task for both stimulus sets was assessed and correlated with the stimulus structure of the standard stimulus. Although there were significant group differences in speed of matching or encoding, matching times for retarded and nonretarded subjects for each stimulus were correlated .97 and .90 for each stimulus set. Correlations of matching times with the stimulus structure variables for each stimulus were very similar for both subject groups. We concluded that both groups encode stimuli in similar ways, but at different rates.

Publisher Summary This chapter investigates the applications and research on computer- assisted instruction (CAI) for the mentally retarded and evaluates the extent to which individualization has been addressed. CAI can be short, cartoonlike educational games or semester-long, text-based question-and-answer instruction. The type of CAI that is based on discovery learning is referred to as simulation. This type of CAI gives the student a goal to reach or a problem to solve and requires the student to learn concepts through trial and error. For example, the ongoing simulation “Oligopoly” requires business students to operate a chocolate firm in an oligopolistic market, given certain market conditions and business choices. The motivational approach to CAI is to make boring instruction fun by making it a game, which will keep students engaged in instruction longer. Some concern has been expressed, however, that the extrinsic motivation provided by the computer game might undermine any intrinsic interest a student might have in the subject matter. If CAI is to provide individualized instruction, then it might benefit from what is known about one-to-one tutoring, an individualized form of instruction which is the most effective form of instruction. Research in CAI programming for mentally retarded people is needed in two main areas-methods for individualizing CAI and methods that address group characteristics of the mentally retarded.

Epitaxial, lattice-matched GaAs/Ca0.45Sr0.55/F2 heterostructures were grown on Ge(100) substrates by molecular beam epitaxy. The films were analyzed by Rutherford backscattering and secondary ion mass spectroscopy to determine crystallinity and Ge outdiffusion. The Xmin (channeling over random yield) of a 1.5 μm-thick GaAs film grown on the fluoride is 0.075, indicating reasonably good epitaxy. After rapid thermal annealing, the crystallinity of higher-Xmin films improves, and Ge diffuses only 200 A into the fluoride, indicating that a thin fluoride layer is an effective barrier to Ge outdiffusion.

Abstract: Several different types of GaAs-AlGaAs heterostructures were grown on Si substrates by MOCVD. The defect density in as-grown samples (~108cm−2) was similar to that of GaAs layers grown directly on Si, and the crystalline quality of the material was observed to improve slightly with post-growth annealing at 900°C. We examined the diffusion of both Si and Zn dopants during this type of annealing and found only a small amount of redistribution of both species. Laser annealing of GaAs-on-Si was also examined as a method of reducing the defect density in the material - we observed substantial improvements in surface quality, but no change in sub-surface crystalline quality.

The rareness of false arterial aneurysm, a consequence of a non-penetrating injury of a limb, induced the Authors, on the basis of the most recent literature, to review its physiopathologic, clinical and therapeutical aspects, with the purpose to hasten its diagnosis and prevent its complications through the adoption of the most suitable surgical treatment.

Skin cancer is relatively uncommon among black individuals. Squamous cell carcinoma occurred in a scar of chronic discoid lupus erythematosus in a black patient. A review of 7 previously reported cases of squamous cell carcinoma in blacks with chronic discoid lupus erythematosus indicates a tendency of the cancer to metastasize. Sun exposure of the hypopigmented lesions of chronic discoid lupus and possibly other factors predispose to cancer of the skin. Poorly healing skin lesions in chronic discoid lupus should arouse suspicion of malignant change.

A case of mesenteric lymphadenitis due to Yersinia pseudotuberculosis type I is described in a young adult. The diagnosis is suggested by histological appearance and confirmed by serological tests. Histological and semithin sections reveal granulomas with central microabscesses and concentric coagulative necrosis. By histochemical and immunohistochemical techniques, fibrinogen/fibrin deposits are observed as a prominent intercellular meshwork around microabscesses or as loosely intertwining strands in small granulomas. Electron microscopy shows fibrinogen/fibrin deposits closely associated both fibrous long-spacing (FLS) fibers and thin collagen fibers. The pathogenesis and type of granuloma as well as the significance of fibrinogen/fibrin deposits are discussed with reference to current literature.

GaAs layers were grown directly on misoriented (2° off (100)→[011]) Si substrates by Metalorganic Chemical Vapor Deposition. The threading dislocation density at the surface of 4 μm thick layers was typically 108cm−2, as determined by both preferential etching and transmission electron microscopy. Rapid thermal annealing (900°C, 10s) improved the crystalline quality of the GaAs near the heterointerface while allowing no detectable Si diffusion into this layer. Two deep electron traps were observed in the undoped GaAs, but were present at a low concentration (∼ 1013 cm−3 ). The (400) x-ray diffraction peak width from the GaAs was significantly reduced with increasing GaAs layer thickness, indicating improved material quality. This is supported by Si implant activation data, which shows higher net donor activity in thicker layers.

RANTES plays a crucial role in cell recruitment in allergic inflammation. We investigated the pharmacological modulation of RANTES release in cultured peripheral blood mononuclear cells obtained from allergic patients with active asthma. Chemokine production was assessed before and after 15 day treatment with histamine-1 receptor antagonists (antihistamines) (Loratadine or Cetirizine) and a steroid (Deflazacort), both in unstimulated and PHA-stimulated cell cultures. Results were compared with those obtained from placebo-treated patients. During the treatment period, patients recorded morning and evening peak expiratory flow (PEF) by the mini-Wright procedure. PEF absolute values and diurnal variability significantly improved respect to the pre-treatment in steroid-treated patients, in comparison to the placebo and antihistamine-treated groups (p#x003C;0.001 and 0.01, respectively). PEF diurnal variability in the antihistamine-treated group were lower than placebo-treated group without statistical significance (p=0.06). No differences could be found in RANTES levels in supernatants of all cultures between the two antihistamines. RANTES release significantly decreased in supernatants of all cell cultures from steroid (p#x003C;0.01) and antihistamine (p=0.03 and 0.04) groups after treatments, compared to the basal values; whereas it increased slightly in controls. Co-variance analysis on RANTES levels, adjusting for pre-treatment values, showed a significant reduction of RANTES release by PHA-stimulated PBMCs from steroid (p=0.003) and anti-histamine (p=0.03) groups, with respect to the placebo group. The same statistical tool applied between the steroid and the antihistamine groups showed, after therapy, the lowest levels of RANTES to be associated with steroid treatment (p=0.005). The study shows that the steroid is the most effective drug in modulating RANTES release from PBMCs. However, antihistamines, which are able to reduce cell recruitment due to chemokine release, avoiding important side effects, may be useful in long term therapy in controlling and preventing allergic inflammation.

Microsatellite replication errors (RERs), consisting in random tumour-associated allele contractions or expansions, represent a frequent genetic alteration in gastric cancer and appear to be associated with important clinicopathologic parameters. To verify the role of microsatellite instability in the initial phases of gastric carcinogenesis, we analysed the status of II microsatellites in paired microdissected samples of tumour and unaffected mucosa from 30 cases of early gastric carcinoma. Fifteen tumours (50%) demonstrated RERs: these included 7 cases with RERs at one locus and 8 cases with RERs at 2 or more loci. Cases with 2 or more RERs were more frequent among intramucosal tumours, compared to tumours with submucosal spread (43% vs. 12%) and among tumours staged T1NOMx, compared to tumours staged T1N1Mx (35% vs. 0%). RER-positive microsatellite typings were statistically more frequent among tumours with intramucosal extension, lower stage (T1NOMx) and excavated growth pattern (macroscopic type III), compared to tumours with submucosal extension, higher stage (T1N1Mx) and elevated, flat or depressed growth patterns (macroscopic types IIa-IIb-IIc respectively). The above findings indicate that microsatellite instability occurs early in the progression of sporadic gastric cancer and tends to be associated with good prognostic indicators.

INTRODUCTION Robotic surgery has gained wide acceptance in recent years. However its development is slower and the lack of high level experience with this technique is an important limitation. This manuscript discusses some of the reasons of it and aims to describe the organizational system we have progressively established in our center in order to improve the development of Robotic program in our surgical area. METHODS Some points may be required to improve the robotic program development in a general surgical department, including: a broad availability of robotic system in a surgical area; an ideal setting area with mainly oncological and hepato-biliary-pancreatic disease; the need of a mainly young team; a broad application of the robotic system in more general surgical fields; a high motivation on robotic use; a departmental and institutional economical effort. We have tried to achieve these goals before starting the robotic program in our department at October 2010. RESULTS From October 2010 until November 2013 a total of 170 procedures have been performed, 92% of them for malignant diseases. Conversion rate and overall morbidity was 5% and 19%, respectively. CONCLUSIONS The organizational model defined in our center is facilitating the constant and progressive development of the robotic program. A broad and flexible availability of the robotic system, a progressive increase of young surgeons joining this technology as well as the institutional and departmental economical effort are the points with which the robotic system may increase its development in a surgical department.

The growth of GaAs layers on silicon substrates is under extensive investigation with a view to achieving the integration of GaAs-based optoelectronic devices with Si integrated circuit technology. The large lattice mismatch between Si and GaAs (-4%) together with the differences in the thermal expansion coefficients between the two materials results in a highly stressed interface. Several different approaches have been undertaken in attempts to reduce the dislocation density of the GaAs layer. The inclusion of graded composition GaAsP ‘buffer’ layers, intermediate Ge layers and the inclusion of strained layer superlattices in the growth regime have been reported by many workers. Growth of GaAs directly on Si has been reported to yield GaAs heteroepitaxial films suitable for electronic applications such as FETs and low threshold AlGaAs/GaAs double heterostructure injection lasers.