Polarity in GaN and ZnO: Theory, measurement, growth, and devices

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Rev. 3, 041303 (2016) and may be found at https://doi.org/10.1063/1.4963919.The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade

La peste negra bajomedieval (1348-1351 AD) en el valle del Tiétar (sierra de Gredos, Ávila): aspectos económicos y paleoambientales

En el presente trabajo se evalúan los efectos de la peste negra bajomedieval (1348–1351 AD) sobre los bosques y las actividades agroforestales de un valle intramontano de la Meseta sur española, a partir de análisis polínicos de alta resolución. Para comprender mejor los efectos de aquella pandemia se analiza la secuencia paleoambiental de cinco turberas, a lo largo de un amplio recorrido cronológico entre los siglos XII y XIV. Este análisis demuestra que la peste provocó una desaceleración de las actividades agropecuarias –agricultura, arboricultura, ganadería– y la consiguiente recuperación de las masas forestales, salvo en las zonas de montaña donde un menor control de los pasos ganaderos incidió en cierta degradación del bosque.1 Introducción 2 Área de estudio y metodología 2.1 El valle del Tiétar en la provincia de Ávila 2.2 Registros polínicos fósiles 3 Resultados y discusión 3.1 Antes de la pandemia (1200–1348 AD) 3.2 La epidemia de peste negra en la sierra de Gredos (1348–1351 AD) 3.3 Recuperación tras la pandemia (1351–1400 AD) 4 Conclusione

Palaeoenvironmental History of the Gredos Range (Spanish Central System, Avila) in Visigothic Times: The Impact of the Justinianic Plague (AD 541–543)

This paper evaluates the possible impact of the early medieval pandemic known as the “Justinianic plague” as one of the factors that shaped the mountain ecosystems in the Spanish Central System of the Iberian Peninsula. For this purpose, we focus on two high-resolution, radiocarbon-dated natural pollen records from the Gredos Range (Avila). These cores frame the information they offer within the general picture of the socio-political and environmental transformations of Late Antiquity. Along these three centuries, between c. AD 400 and AD 720, the palynological sequence allows us to recognize eight short phases (on a ten-year and even five-year scale) through which the forest formations traversed. This analysis has made it possible to identify olive and chestnut tree arboriculture since the beginning of the studied interval, as well as to characterize the fluctuation in the thinning processes of the high montane pine forests, due to slash-and-burn practices to open pastures, especially from the permanent occupation of the piedmont in Visigothic times (c. AD 450). The sequence also shows a significant decrease in the anthropic signal during a short period (c. AD 540-545) that can be disassociated from the early effects of the Late Antique Little Ice Age (c. AD 450-660) and which is possibly more related to the plague, as evidenced by the subsequent recovery of anthropic pressure on the pine forest and the extension of the olive and chestnut grove in the 6th and 7th centuries AD.El presente trabajo evalúa la posible influencia de la pandemia altomedieval conocida como «plaga de Justiniano» como uno de los factores que contribuyeron a configurar los ecosistemas de montaña enclavados en el Sistema Central de la península ibérica. Para ello, el artículo se centra en dos registros polínicos naturales de alta resolución y bien datados mediante radiocarbono, obtenidos en la Sierra de Gredos (Ávila), y enmarca la información que ofrecen en el cuadro general de las dinámicas sociopolíticas y ambientales de la Antigüedad Tardía. En el intervalo de tres siglos, entre c. 400 y 720 A. D., la secuencia palinológica permite reconocer ocho fases breves (de escala decenal e incluso quinquenal) que marcaron las transformaciones del paisaje. Este análisis ha posibilitado identificar la implantación de la arboricultura de olivo y castaño desde el inicio del intervalo estudiado, así como caracterizar la fluctuación en los procesos de clareo de los pinares altimontanos, por la incidencia de talas y rozas con fuego para abrir pastizales, especialmente desde la ocupación permanente del piedemonte en época visigoda (c. 450 A. D.). La secuencia analizada muestra un significativo aminoramiento de la señal antrópica durante un breve intervalo (c. 540-545 A. D.) que cabe desvincular de los efectos tempranos de la Pequeña Edad de Hielo tardoantigua (c. 450-660 A. D.) y resulta más plausible relacionar con la plaga, como avala la subsiguiente recuperación de la presión antrópica sobre el pinar y la extensión del olivar y el castañar en los siglos VI y VII A. D.- Introducción - Zona de estudio - Consideraciones metodológicas - Historia de la vegetación e impacto humano (400-720 A.D.) - Conclusiones, variabilidad climática y efectos de la pandemia (541-543 A.D.

A Peer-reviewed Newspaper About_ Excessive Research

Research on machines, research with machines, and research as a machine. Publication resulting from research workshop at Exhibition Research Lab, Liverpool John Moores University, organised in collaboration with Liverpool John Moores University and Liverpool Biennial, and transmediale festival for art and digital culture, Berlin

Predictors of Nodal and Metastatic Failure in Early Stage Non-Small Cell Lung Cancer after Stereotactic Body Radiation Therapy

Introduction/Background Many early-stage non-small cell lung cancer (ES-NSCLC) patients undergoing stereotactic body radiation therapy (SBRT) develop metastases, which is associated with poor outcomes. We sought to identify factors predictive of metastases after lung SBRT and created a risk stratification tool. Materials and Methods We included 363 patients with ES-NSCLC who received SBRT; median follow-up was 5.8 years. The following patient and tumor factors were retrospectively analyzed for their association with metastases (defined as nodal and/or distant failure): sex; age; lobe involved; centrality; previous NSCLC; smoking status; gross tumor volume (GTV); T-stage; histology; dose; minimum, maximum, and mean GTV dose; and parenchymal lung failure. A metastasis risk-score linear-model using beta coefficients from a multivariate Cox model was built. Results A total of 111/406 (27.3%) lesions metastasized. GTV volume and dose were significantly associated with metastases on univariate and multivariate Cox proportional hazards modeling (p<0.001 and HR=1.02 per mL, p<0.05 and HR=0.99 per Gy, respectively). Histology, T-stage, centrality, lung parenchymal failures, and previous NSCLC were not associated with development of metastasis. A metastasis risk-score model using GTV volume and prescription dose was built: [risk score=(0.01611 x GTV)–(0.00525 x dose (BED10))]. Two risk-score cutoffs separating the cohort into low-, medium-, and high-risk subgroups were examined. The risk-score identified significant differences in time to metastases between low-, medium-, and high-risk patients (p<0.001), with 3-year estimates of 81.1%, 63.8%, and 38%, respectively. Conclusion GTV volume and radiation dose are associated with time to metastasis and may be used to identify patients at higher risk of metastasis after lung SBRT

Stable isotope-assisted untargeted metabolomics identifies ALDH1A1-driven erythronate accumulation in lung cancer cells

Using an untargeted stable isotope-assisted metabolomics approach, we identify erythronate as a metabolite that accumulates in several human cancer cell lines. Erythronate has been reported to be a detoxification product derived from off-target glycolytic metabolism. We use chemical inhibitors and genetic silencing to define the pentose phosphate pathway intermediate erythrose 4-phosphate (E4P) as the starting substrate for erythronate production. However, following enzyme assay-coupled protein fractionation and subsequent proteomics analysis, we identify aldehyde dehydrogenase 1A1 (ALDH1A1) as the predominant contributor to erythrose oxidation to erythronate in cell extracts. Through modulating ALDH1A1 expression in cancer cell lines, we provide additional support. We hence describe a possible alternative route to erythronate production involving the dephosphorylation of E4P to form erythrose, followed by its oxidation by ALDH1A1. Finally, we measure increased erythronate concentrations in tumors relative to adjacent normal tissues from lung cancer patients. These findings suggest the accumulation of erythronate to be an example of metabolic reprogramming in cancer cells, raising the possibility that elevated levels of erythronate may serve as a biomarker of certain types of cancer

Precision Measurement of the First Ionization Potential of Nobelium

One of the most important atomic properties governing an element’s chemical behavior is the energy required to remove its least-bound electron, referred to as the first ionization potential. For the heaviest elements, this fundamental quantity is strongly influenced by relativistic effects which lead to unique chemical properties. Laser spectroscopy on an atom-at-a-time scale was developed and applied to probe the optical spectrum of neutral nobelium near the ionization threshold. The first ionization potential of nobelium is determined here with a very high precision from the convergence of measured Rydberg series to be 6.626   21 ± 0.000   05     eV . This work provides a stringent benchmark for state-of-the-art many-body atomic modeling that considers relativistic and quantum electrodynamic effects and paves the way for high-precision measurements of atomic properties of elements only available from heavy-ion accelerator facilities

Major histocompatibility complex class I molecules protect motor neurons from astrocyte-induced toxicity in amyotrophic lateral sclerosis

Astrocytes isolated from individuals with amyotrophic lateral sclerosis (ALS) are toxic to motor neurons (MNs) and play a non–cell autonomous role in disease pathogenesis. The mechanisms underlying the susceptibility of MNs to cell death remain unclear. Here we report that astrocytes derived from either mice bearing mutations in genes associated with ALS or human subjects with ALS reduce the expression of major histocompatibility complex class I (MHCI) molecules on MNs; reduced MHCI expression makes these MNs susceptible to astrocyte-induced cell death. Increasing MHCI expression on MNs increases survival and motor performance in a mouse model of ALS and protects MNs against astrocyte toxicity. Overexpression of a single MHCI molecule, HLA-F, protects human MNs from ALS astrocyte–mediated toxicity, whereas knockdown of its receptor, the killer cell immunoglobulin-like receptor KIR3DL2, on human astrocytes results in enhanced MN death. Thus, our data indicate that, in ALS, loss of MHCI expression on MNs renders them more vulnerable to astrocyte-mediated toxicity