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Our understanding of the complex relationship between schizophrenia symptomatology and etiological factors can be improved by studying brain-based correlates of schizophrenia. Research showed that impairments in value processing and executive functioning, which have been associated with prefrontal brain areas [particularly the medial orbitofrontal cortex (MOFC)], are linked to negative symptoms. Here we tested the hypothesis that MOFC thickness is associated with negative symptom severity.
This study included 1985 individuals with schizophrenia from 17 research groups around the world contributing to the ENIGMA Schizophrenia Working Group. Cortical thickness values were obtained from T1-weighted structural brain scans using FreeSurfer. A meta-analysis across sites was conducted over effect sizes from a model predicting cortical thickness by negative symptom score (harmonized Scale for the Assessment of Negative Symptoms or Positive and Negative Syndrome Scale scores).
Meta-analytical results showed that left, but not right, MOFC thickness was significantly associated with negative symptom severity (βstd = −0.075; p = 0.019) after accounting for age, gender, and site. This effect remained significant (p = 0.036) in a model including overall illness severity. Covarying for duration of illness, age of onset, antipsychotic medication or handedness weakened the association of negative symptoms with left MOFC thickness. As part of a secondary analysis including 10 other prefrontal regions further associations in the left lateral orbitofrontal gyrus and pars opercularis emerged.
Using an unusually large cohort and a meta-analytical approach, our findings point towards a link between prefrontal thinning and negative symptom severity in schizophrenia. This finding provides further insight into the relationship between structural brain abnormalities and negative symptoms in schizophrenia.
We present the first 12CO 1→0 emission-line maps of the vicinities of two Wolf-Rayet stars (WR 16 and WR 75) and their associated ring nebulae. We illustrate that sizeable amounts of molecular gas appear associated with these ring nebulae and therefore that the mass of gas in ring nebulae is significantly higher than inferred from observations of the ionized gas component alone. We discuss the possible stellar and interstellar origins of these molecular materials and the implications for the evolution of massive stars up to the WR phase.
We have observed 2 compact PPNe, AFGL 2343 and IRAS 22272+5435, in the CO J=1-0 transition using the Owens Valley interferometer (OVRO), and the NRAO 12-meter telescope. Our observations were made in the low and intermediate resolution configurations of the interferometer and we obtain a synthesized beam (HPBW) of ≃ 4″. We are now modelling both sources using statistical equilibrium/radiative transfer codes. Our objectives are to a) map the distribution and kinematics of the molecular gas at high angular resolution and b) estimate the physical conditions (mass loss rate, temperature, density) in the molecular envelopes, through our models.
On December 10, 2014, the United Nations General Assembly adopted the United Nations Convention on Transparency in Treaty-based Investor-State Arbitration, also known as the Mauritius Convention on Transparency, which was prepared by the United Nations Commission on International Trade Law (UNCITRAL). The Mauritius Convention is intended to provide states with an efficient mechanism for applying the UNCITRAL Rules on Transparency in Treaty-based Investor-State Arbitration (Transparency Rules) in investor-state arbitrations arising under investment treaties concluded before the Transparency Rules’ effective date of April 1, 2014. The Mauritius Convention was opened for signature on March 17, 2015, in Port Louis, Mauritius.
Optical and tactile single scanning probes usually are used in dimensional metrology
applications, especially for roughness, form, thickness and surface profile measurements.
To perform assessments with nanometre level of accuracy, specific ultra-high precision
machines have been developed by the National Metrology Institutes (NMIs) such as the LNE,
VSL, METAS, SMD, generally in collaboration with industrials and academics partners. Such
developments are not devoted only to NMIs but many industrials develop and commercialize
their own ultra-high precision machines as the IBSPE and TNO companies. All these machines
provide optical and tactile precise measurements and cover a large domain of application
such as the form’s characterization of optical lenses. In this paper the performance and
capability of ultra-high precision machines of some National Metrology Institutes (LNE,
VSL, SMD and METAS) and industrials companies (TNO and IBSPE), involving together in the
IND10 European EMRP project titled “Optical and tactile metrology for absolute form
characterization”, will be detailed. Theirs probing systems and accuracies levels will be
evoked. Relevant results especially for measuring optical lenses will be also presented
We present a study of the radiative recombination in In0.15Ga0.85N/GaN multiple quantum well samples, where the conditions of growth of the InGaN quantum layers were varied in terms of growth temperature (< 800 °C) and donor doping. The photoluminescence peak position varies strongly (over a range as large as 0.3 eV) with delay time after pulsed excitation, but also with donor doping and with excitation intensity. The peak position is mainly determined by the Stark effect induced by the piezoelectric field. In addition potential fluctuations, originating from segregation effects in the InGaN material, from interface roughness, and the strain fluctuations related to these phenomena, play an important role, and largely determine the width of the emission. These potential fluctuations may be as large as 0.2 eV in the present samples, and appear to be important for all studied growth temperatures for the InGaN layers. Screening effects from donor electrons and excited electron-hole pairs are important, and account for a large part of the spectral shift with donor doping (an upward shift of the photoluminescence peak up to 0.2 eV is observed for a Si donor density of 2 × 1018 cm−3 in the well), with excitation intensity and with delay time after pulsed excitation (also shifts up to 0.2 eV). We suggest a two-dimensional model for electron- and donor screening in this case, which is in reasonable agreement with the observed data, if rather strong localization potentials of short range (of the order 100 Å) are present. The possibility that excitons as well as shallow donors are impact ionized by electrons in the rather strong lateral potential fluctuations present at this In composition is discussed
In0.1Ga0.9N/In0.01Ga0.99N multiple quantum wells (MQWs) with heavily Si-doped barriers, grown with Metal Organic Vapor Phase Epitaxy (MOVPE) at about 8000C, have been studied in detail with optical spectroscopy. Such structures are shown to be very sensitive to a near surface depletion field, and if no additional layer is grown on top of the MQW structure the optical spectra from the individual QWs are expected to be drastically different. For a sample with 3 near surface QWs and Si-doped barriers, only the QW most distant from the surface is observed in photoluminescence (PL). The strong surface depletion field is suggested to explain these results, so that the QWs closer to the surface cannot hold the photo-excited carriers. A similar effect of the strong depletion field is found in an LED structure where the MQW is positioned at the highly doped n-side of the pn-junction. The internal polarization induced electric field in the QWs is also rather strong, and incompletely screened by carriers transferred from the doped barriers. The observed PL emission for this QW is of localized exciton character, consistent with the temperature dependence of peak position and PL decay time. The excitonic lineshape of 35-40 meV in the QW PL is explained as caused by a combination of random alloy fluctuations and interface roughness; the corresponding localization potentials are also responsible for the localization of the excitons in the low temperature range (<150 K). These samples show no evidence of localization due to nanoscale In fluctuations, these commonly observed problems are concluded to be not present in our samples. A second PL feature at lower energy, observed at low temperatures, is shown to be related to an electron pocket at the interface to the underlying n-GaN buffer layer in these samples.
Optical spectra on free exciton properties for GaN are presented and discussed, in particular the influence of epitaxial strain and temperature. The exciton-phonon coupling is also manifested via the temperature dependence of the LO phonon replicas of the free exciton.
We present a study of the radiative recombination in In0.15Ga0.85N/GaN multiple quantum well samples, where the conditions of growth of the InGaN quantum layers were varied. The piezoelectric field as well as short range potential fluctuations are screened via different mechanisms by donor electrons and excited electron-hole pairs. These effects account for a large part of the spectral shift with donor doping (an upward shift of the photoluminescence (PL) peak up to 0.2 eV is observed for a Si donor density of 2 × 1018 cm−3 in the well), with excitation intensity and with delay time after pulsed excitation (also shifts up to 0.2 eV). It appears like 2-dimensional screening of short range potential fluctuations is needed to fully explain the data. We suggest that excitons as well as shallow donors are at least partly impact ionized by electrons in the rather strong lateral potential fluctuations.
Photoluminescence spectra were measured for 100 Å wurtzite GaN AlGaN modulation doped quantum wells. Three well-resolved peaks originate from the quantum well. The theoretically calculated confinement energies have been compared to the experimental energy positions and found to be in good agreement with the data, assuming that the piezoelectric field is largely screened by the electron gas. The highest energy transition may originate from the Fermi edge, consistent with the temperature dependence of the photoluminescence. Decay times for the different transitions indicate that the photoexcited holes are localized.
In their focal article, Ruggs et al. (2013) outline the missed opportunities for researchers within industrial–organizational (I–O) psychology in examining marginalized employees. The authors identify seven groups as having been overlooked by I–O psychologists and thus deserving greater attention in the future. They conclude their focal article by noting that, “Instead of being on the front line serving as scientists and allies for those who are marginalized and treated poorly, we have let these individuals take a backseat while we have gone fishing.” We disagree with this assertion. It is not that we have gone fishing and ignored marginalized employees. Rather, we have gone fishing, in rough waters, to locate hard-to-find fish. We are not purposefully ignoring marginalized employees. On the contrary, we are conducting research while battling numerical representation issues and ethical and administration issues. The focus of our commentary is to highlight these challenges and offer suggestions for addressing them in an effort to assist researchers in actually doing what the authors of the focal article are calling for them to do—to successfully engage in more focused research on these under-represented members of the workforce.
We report an adolescent with a benign cardiac haemangioma with attachments exclusively to the anterior leaflet of the mitral valve. On the basis of our review of the literature, this study has not been reported previously.
We have observed electroluminescence from 4H-SiC Ni-Schottky diodes on 1015cm−3 nitrogen doped n-type epilayers. A high barrier Schottky contact will form an inversion layer close to it. This creates minority carriers that can be injected into the epi and recombine to emit light. The spectral composition and its temperature dependence have been investigated from liquid He temperatures to room temperature. Band edge luminescence, Al related luminescence and DI bound exciton have been observed. To study the electroluminescence from Schottky diodes provides an easy and additional technique for defect characterization of epitaxial layers.
An intrinsic defect spectrum, commonly observed after ion-implantation, electron, proton or neutron irradiation and even after SIMS measurements is investigated using photoluminescence techniques. The spectrum is associated with carbon related isoelec-tronic centers having a pseudodonor like behaviour. Vacancy-interstitial pair complexes are tentatively suggested as the defect centers responsible for this intrinsic spectrum.
In0.11Ga0.89N/In0.01Ga0.99N multiple quantum wells (MQWs) with heavily Si-doped barriers are shown to be very sensitive to a near surface depletion field. For a sample with 3 QWs, similar to what is often used in LEDs, only the QW most distant from the surface is observed in photoluminescence (PL). The appearance of a second lower energy PL peak below the ordinary QW exciton peak is a proof of a substantial band bending across the MQW structure. A similar effect seems to occur in pn-junctions having an MQW in the depletion region of a highly doped n-side. The strong depletion field is suggested to explain these results. The apparent absence of PL from the QWs closer to the surface (pn-junction) is tentatively ascribed to a loss of hole confinement in the strong depletion field.
We report low temperature photoluminescence (PL) spectra related to a two-dimensional electron gas confined at a GaN/AlGaN heterointerface. The recombination between electrons confined in the bottom of the interface potential and photoexcited holes causes a broad PL emission about 50 meV below the bulk GaN exciton emission. A second emission, attributed to the recombination of electrons in the first excited level at the interface, is also observed close to the excitonic band gap in GaN. The data agrees with a self consistent calculation of the energy levels and the electron concentration at the interface. Similar PL data from a modulation doped AlGaN/GaN quantum well exhibit three PL emissions related to the 2D electron gas.
We have performed time resolved photoluminescence measurements of the exciton recombination in different GaN samples at low temperatures. In epitaxial layers the decay time of the free exciton is typically faster than 100 ps. This is due to a dominating non-radiative recombination process. In thick bulk samples we have resolved and measured the decay time of the free exciton with a value of about 200 ps. We believe that this value is close to the radiative lifetime for free excitons in GaN. We have also shown that excitation transfer occurs between free and bound exciton states. We have furthermore measured the decay of the donor and acceptor bound excitons, and obtained values of the decay time of 250 ps and 1200 ps, respectively.
The coalescence process has been studied in four different hyper-monotectic Zn-Bi alloys with 4–10wt % Bi . The alloys have been studied by isothermal treatments at a temperature just above the monotectic temperature and at different holding times. The alloys have been studied both at microgravity and at normal gravity. The change of the particle distribution as a function of composition and holding time has been investigated. The changing of the particle distribution has been compared with the theory of particle collision. The validity of the collision theory is investigated with respect to the theory of liquid phase sintering.
Unidirectional solidification experiments with monotectic and near monotectic Cu-Pb alloys have been performed with the growth direction both parallel and antiparallel to the gravity vector. It was found that a more regular composite structure was possible to achieve in the samples solidified parallel to the gravity vector. It was also found that the amount of lead rich phase, regularily incorporated in the structure, was less than one would expect theoretically. It is proposed that monotectic alloys can solidify to two different kinds of composite structures. One, which can be described by the theory of coupled growth of a rod eutecticum, and the other similar to the growth of primary rods.
We present an optical study of the excitonic properties of epitaxial GaN using reflectivity and photoluminescence (PL) measurements. The values for the intrinsic exciton energies are found to be dependent on the built in strain developed due to the difference in thermal expansion coefficients between the GaN epilayer and the foreign substrate. For GaN on sapphire thecompressive biaxial strain causes an upshift of A and B excitons by typically 15 meV relative to the strain free sample, in accordance with previous data. For GaN on SiC, on the other hand, a downshift ˜ 8 meV in the free exciton energies is observed at 2K. Only two excitonic peaks about 18 meV apart, are resolved in reflectivity spectra for GaN on SiC, probably due to the overlapping of A and B excitons. The suggested explanation implies the reduction of the bandgap energy and of the valence band splitting under the action of a biaxial tensional strain in the GaN layer. For all structures the strain-induced shifts of the bandgap energy are much smaller at elevated temperatures, presumably reflecting the temperature dependence of the accumulated strain energy. The exciton-polariton structure of the GaN is also discussed. The enhanced intensity of the no-phonon (NP) A line compared to its longitudinal (LO) phonon replica is suggested to be partially attributed to strong defect scattering.