Nanoporous GaN by selective area sublimation through an epitaxial nanomask: AlN versus SixNy.

Nanoporous GaN layers were fabricated using selective area sublimation through a self-organized AlN nanomask in a molecular beam epitaxy reactor. The obtained pore morphology, density and size were measured using plan-view and cross-section scanning electron microscopy experiments. It was found that the porosity of the GaN layers could be adjusted from 0.04 to 0.9 by changing the AlN nanomask thickness and sublimation conditions. The room temperature photoluminescence properties as a function of the porosity were analysed. In particular, a strong improvement (>100) of the room temperature photoluminescence intensity was observed for porous GaN layers with a porosity in the 0.4-0.65 range. The characteristics of these porous layers were compared to those obtained with a SixNynanomask. Furthermore, the regrowth of p-type GaN on light emitting diode structures made porous by using either an AlN or a SixNynanomask were compared.

Nanoscale structural and electrical properties of graphene grown on AlGaN by catalyst-free chemical vapor deposition.

The integration of graphene (Gr) with nitride semiconductors is highly interesting for applications in high-power/high-frequency electronics and optoelectronics. In this work, we demonstrated the direct growth of Gr on Al0.5Ga0.5N/sapphire templates by propane (C3H8) chemical vapor deposition at a temperature of 1350 °C. After optimization of the C3H8 flow rate, a uniform and conformal Gr coverage was achieved, which proved beneficial to prevent degradation of AlGaN morphology. X-ray photoemission spectroscopy revealed Ga loss and partial oxidation of Al in the near-surface AlGaN region. Such chemical modification of a ∼2 nm thick AlGaN surface region was confirmed by cross-sectional scanning transmission electron microscopy combined with electron energy loss spectroscopy, which also showed the presence of a bilayer of Gr with partial sp2/sp3 hybridization. Raman spectra indicated that the deposited Gr is nanocrystalline (with domain size ∼7 nm) and compressively strained. A Gr sheet resistance of ∼15.8 kΩ sq-1 was evaluated by four-point-probe measurements, consistently with the nanocrystalline nature of these films. Furthermore, nanoscale resolution current mapping by conductive atomic force microscopy indicated local variations of the Gr carrier density at a mesoscopic scale, which can be ascribed to changes in the charge transfer from the substrate due to local oxidation of AlGaN or to the presence of Gr wrinkles.

Clinical, functional and genetic characterization of 16 patients suffering from chronic granulomatous disease variants - identification of 11 novel mutations in CYBB.

Chronic granulomatous disease (CGD) is a rare inherited disorder in which phagocytes lack nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. The most common form is the X-linked CGD (X91-CGD), caused by mutations in the CYBB gene. Clinical, functional and genetic characterizations of 16 CGD cases of male patients and their relatives were performed. We classified them as suffering from different variants of CGD (X910 , X91- or X91+ ), according to NADPH oxidase 2 (NOX2) expression and NADPH oxidase activity in neutrophils. Eleven mutations were novel (nine X910 -CGD and two X91- -CGD). One X910 -CGD was due to a new and extremely rare double missense mutation Thr208Arg-Thr503Ile. We investigated the pathological impact of each single mutation using stable transfection of each mutated cDNA in the NOX2 knock-out PLB-985 cell line. Both mutations leading to X91- -CGD were also novel; one deletion, c.-67delT, was localized in the promoter region of CYBB; the second c.253-1879A>G mutation activates a splicing donor site, which unveils a cryptic acceptor site leading to the inclusion of a 124-nucleotide pseudo-exon between exons 3 and 4 and responsible for the partial loss of NOX2 expression. Both X91- -CGD mutations were characterized by a low cytochrome b558 expression and a faint NADPH oxidase activity. The functional impact of new missense mutations is discussed in the context of a new three-dimensional model of the dehydrogenase domain of NOX2. Our study demonstrates that low NADPH oxidase activity found in both X91- -CGD patients correlates with mild clinical forms of CGD, whereas X910 -CGD and X91+ -CGD cases remain the most clinically severe forms.

Tuning electrical and thermal conductivities of the two-dimensional electron gas in AlN/GaN heterostructures by piezoelectricity.

We investigate the electrical and thermal conductivities of the two-dimensional electron gas (2DEG) confined in the quantum well formed at the heterojunction between a thin GaN layer and an AlN layer strained by an Al x Ga1-x N capping layer in the temperature range from 10 to 360 K. The experimental protocol developed to deduce from calorimetric and Hall-effect measurements at a variable temperature the critical characteristics and transport properties of the confined 2DEG is presented. It is found that, in the measured temperature range (10-360 K), the electrical conductivity of the 2DEG is temperature-independent, due to the predominance of scattering processes by interface defects. However, the thermal conductivity shows a linear temperature dependence, mirroring the specific heat of free electrons. The temperature-independent relaxation time associated with the overall electron scattering means that the values obtained for electrical and thermal conductivities are in excellent agreement with those stipulated by the Weidemann-Franz law. It is also found that for weak strain fields in the AlN layer, both the electrical and thermal conductivities of the two-dimensional interfacial electrons increase exponentially with strain. The importance of 2DEG in AlN/GaN quantum wells lies in the fact that the strong piezoelectricity of AlN allows the transport properties of the 2DEG to be tuned or modulated by a weak electric field even with the high density of lattice mismatch induced defects at the AlN-GaN interface .

Al5+αSi5+δN12, a new Nitride compound.

The family of III-Nitride semiconductors has been under intensive research for almost 30 years and has revolutionized lighting applications at the dawn of the 21st century. However, besides the developments and applications achieved, nitride alloys continue to fuel the quest for novel materials and applications. We report on the synthesis of a new nitride-based compound by using annealing of AlN heteroepitaxial layers under a Si-atmosphere at temperatures between 1350 °C and 1550 °C. The structure and stoichiometry of this compound are investigated by high resolution transmission electron microscopy (TEM) techniques and energy dispersive X-Ray (EDX) spectroscopy. Results are supported by density functional theory (DFT) calculations. The identified structure is a derivative of the parent wurtzite AlN crystal where the anion sublattice is fully occupied by N atoms and the cation sublattice is the stacking of 2 different planes along <0001>: The first one exhibits a ×3 periodicity along <11-20> with 1/3 of the sites being vacant. The rest of the sites in the cation sublattice are occupied by an equal number of Si and Al atoms. Assuming a semiconducting alloy, a range of stoichiometries is proposed, Al5+αSi5+δN12 with α being between -2/3 and 1/4 and δ between 0 and 3/4.

Comparison of [18F] FDG-PET/MRI and Clinical Findings for Assessment of Suspected Lumbar Facet Joint Pain: A Prospective Study to Characterize Candidate Nonanatomic Imaging Biomarkers and Potential Impact on Management.

BACKGROUND AND PURPOSE: Prior retrospective studies have suggested that both T2 hyperintensity and gadolinium enhancement on fat-suppressed MR imaging are associated with lumbar facet joint pain, but prospective evaluation of FDG-PET/MR imaging with a standardized protocol and correlation to clinical findings are lacking. The primary aim was to prospectively assess a standardized FDG-PET/MRI protocol in patients with suspected facetogenic low back pain, with determination of the concordance of imaging and clinical findings. MATERIALS AND METHODS: Ten patients with clinically suspected facetogenic low back pain were prospectively recruited with a designation of specific facet joints implicated clinically. Subsequently, patients underwent an FDG-PET/MR imaging examination with gadolinium. Each facet joint was graded for perifacet signal change on MR imaging and FDG activity. The frequency and correlation of MR imaging, FDG-PET, and clinical findings were determined. RESULTS: FDG activity showed high concordance with high overall MR imaging scores (concordance correlation coefficient = 0.79). There was concordance of the clinical side of pain with the side of high overall MR imaging scores and increased FDG activity on 12/20 (60%) sides. Both a high overall MR imaging score (concordance correlation coefficient = 0.12) and FDG-PET findings positive for increased activity (concordance correlation coefficient = 0.10) had low concordance with the specific clinically implicated facet joints. Increased FDG activity or high MR imaging scores or both were present in only 10/29 (34%) facet joints that had been clinically selected for percutaneous intervention. Eleven (11%) facet joints that had not been selected for treatment demonstrated these imaging findings. CONCLUSIONS: There was low concordance of perifacet signal change and FDG activity with clinically implicated facet joints. This could indicate either the potential to change patient management or a lack of biomarker accuracy. Therefore, additional larger randomized studies with the use of comparative medial branch blocks would be useful to further investigate the clinical utility of these findings.

Selective Area Sublimation: A Simple Top-down Route for GaN-Based Nanowire Fabrication.

Post-growth in situ partial SiNx masking of GaN-based epitaxial layers grown in a molecular beam epitaxy reactor is used to get GaN selective area sublimation (SAS) by high temperature annealing. Using this top-down approach, nanowires (NWs) with nanometer scale diameter are obtained from GaN and InxGa1-xN/GaN quantum well epitaxial structures. After GaN regrowth on InxGa1-xN/GaN NWs resulting from SAS, InxGa1-xN quantum disks (QDisks) with nanometer sizes in the three dimensions are formed. Low temperature microphotoluminescence experiments demonstrate QDisk multilines photon emission around 3 eV with individual line widths of 1-2 meV.

Wernicke encephalopathy and Creutzfeldt-Jakob disease.

We assessed the prevalence of Wernicke encephalopathy (WE) in all 657 cases suspected of Creutzfeldt-Jakob (CJD) referred from 2001 to 2006 to the French Neuropathology Network of CJD. Clinical, biological and imaging data were reviewed when the diagnosis of WE was made at autopsy. No CJD was found in five cases suspected of sporadic CJD. In these five cases, myoclonus had been observed in four, CSF 14-3-3 protein in two. In 14 other cases, WE was combined with CJD, 13 of which were sporadic. These belonged mainly to the molecular variants of sporadic CJD associated with a long duration of disease. This stresses the necessity of remaining alert to the diagnosis of WE when CJD is suspected.

Protecting the cellular energy state during contractions: role of AMP deaminase.

AMP deaminase activity (AMP->IMP+NH3) is the entry reaction to the purine nucleotide cycle. In skeletal muscle, excessive energy demands during contractions leads to a net production of ADP, because ATP hydrolysis exceeds ADP rephosphorylation. Elevations in ADP increase AMP, via the myokinase reaction. This accumulation of ATP hydrolysis products should lead to a catastrophic reduction in the energy state of the myocyte. The removal of AMP to IMP in times of excessively high energy demands have been hypothesized as essential to protect the energy state of the cell. While AMP deamination leads to a net loss of adenine nucleotides (principally, as ATP), the viability of the myocyte is preserved. Following these demanding contraction conditions, the concentration of IMP of fast-twitch muscle is rapidly reduced, typically with the return of the muscle adenine nucleotide content (ATP + ADP + AMP) to pre-contraction levels. While these observations are generally observed for fast-twitch skeletal muscle and consistent with the hypothesis, there has been no direct experimental evaluation. In the AK1 (-/-) mouse, there is a markedly reduced accumulation of AMP, during conditions of excessive contractile activity. Rather, there is a high ADP concentration, approaching 1.5 mM, that remains unbound 'free' within the muscle. This contributes to an inordinate reduction in the ATP/ADP ratio. At the same time, PCr hydrolysis is nearly complete leading to a large increase in orthophosphate. In combination, this leads to an exceptional decline in the free energy of ATP hydrolysis. This is projected to impair Ca(2+) handling by the sarcoplasmic reticulum and slow cross-bridge cycling rate. The outcome should be slowed contraction characteristics and possible contracture. While some contractile changes were observed, there was a remarkable ability of the muscle to function under these challenging energetic conditions. Thus, it is not essential that the AMP deaminase reaction be operating during intense contraction conditions. This helps explain why patients deficient in AMP deaminase do not always exhibit an impaired muscle function.

Argon I Lines Produced in a Hollow Cathode Source, 332 nm to 5865 nm.

We report precision measurements by Fourier transform spectroscopy of the vacuum wavenumber, line width, and relative signal strength of 928 lines in the Ar I spectrum. Wavelength in air and classification of the transition are supplied for each line. A comparison of our results with other precision measurements illustrates the sensitivity of Ar I wavelengths to conditions in the light source.

Influence of ribose on adenine salvage after intense muscle contractions.

The influence of ribose supplementation on skeletal muscle adenine salvage rates during recovery from intense contractions and subsequent muscle performance was evaluated using an adult rat perfused hindquarter preparation. Three minutes of tetanic contractions (60 tetani/min) decreased ATP content in the calf muscles by approximately 50% and produced an equimolar increase in IMP. Effective recovery of muscle ATP 1 h after contractions was due to reamination of IMP via the purine nucleotide cycle and was complete in the red gastrocnemius but incomplete in the white gastrocnemius muscle section. Adenine salvage rates in recovering muscle averaged 45 +/- 4, 49 +/- 5, and 30 +/- 3 nmol. h(-1). g(-1) for plantaris, red gastrocnemius, and white gastrocnemius muscle, respectively, which were not different from values in corresponding nonstimulated muscle sections. Adenine salvage rates increased five- to sevenfold by perfusion with approximately 4 mM ribose (212 +/- 17, 192 +/- 9, and 215 +/- 14 nmol. h(-1). g(-1) in resting muscle sections, respectively). These high rates were sustained in recovering muscle, except for a small (approximately 20%) but significant (P < 0.001) decrease in the white gastrocnemius muscle. Ribose supplementation did not affect subsequent muscle force production after 60 min of recovery. These data indicate that adenine salvage rates were essentially unaltered during recovery from intense contractions.

Purine salvage to adenine nucleotides in different skeletal muscle fiber types.

Rates of purine salvage of adenine and hypoxanthine into the adenine nucleotide (AdN) pool of the different skeletal muscle phenotype sections of the rat were measured using an isolated perfused hindlimb preparation. Tissue adenine and hypoxanthine concentrations and specific activities were controlled over a broad range of purine concentrations, ranging from 3 to 100 times normal, by employing an isolated rat hindlimb preparation perfused at a high flow rate. Incorporation of [(3)H]adenine or [(3)H]hypoxanthine into the AdN pool was not meaningfully influenced by tissue purine concentration over the range evaluated (approximately 0.10-1.6 micromol/g). Purine salvage rates were greater (P < 0.05) for adenine than for hypoxanthine (35-55 and 20-30 nmol x h(-1) x g(-1), respectively) and moderately different (P < 0.05) among fiber types. The low-oxidative fast-twitch white muscle section exhibited relatively low rates of purine salvage that were approximately 65% of rates in the high-oxidative fast-twitch red section of the gastrocnemius. The soleus muscle, characterized by slow-twitch red fibers, exhibited a high rate of adenine salvage but a low rate of hypoxanthine salvage. Addition of ribose to the perfusion medium increased salvage of adenine (up to 3- to 6-fold, P < 0.001) and hypoxanthine (up to 6- to 8-fold, P < 0.001), depending on fiber type, over a range of concentrations up to 10 mM. This is consistent with tissue 5-phosphoribosyl-1-pyrophosphate being rate limiting for purine salvage. Purine salvage is favored over de novo synthesis, inasmuch as delivery of adenine to the muscle decreased (P < 0.005) de novo synthesis of AdN. Providing ribose did not alter this preference of purine salvage pathway over de novo synthesis of AdN. In the absence of ribose supplementation, purine salvage rates are relatively low, especially compared with the AdN pool size in skeletal muscle.

Partial lumbosacral transitional vertebra resection for contralateral facetogenic pain.

STUDY DESIGN: Case report of surgically treated mechanical low back pain from the facet joint contralateral to a unilateral anomalous lumbosacral articulation (Bertolotti's syndrome). OBJECTIVES: To describe the clinical presentation, diagnostic evaluation, and management of facet-related low back pain in a 17-year-old cheerleader and its successful surgical treatment with resection of a contralateral anomalous articulation. SUMMARY OF BACKGROUND DATA: Lumbosacral transitional vertebrae are common in the general population. Bertolotti's syndrome is mechanical low back pain associated with these transitional segments. Little is known about the pathophysiology and mechanics of these vertebral segments and their propensity to be pain generators. Treatment of this syndrome is controversial, and surgical intervention has been infrequently reported. METHOD: A retrospective chart analysis and radiographic review were performed. RESULTS: Repeated fluoroscopically guided injections implicated a symptomatic L6-S1 facet joint contralateral to an anomalous lumbosacral articulation. Eventually, a successful surgical outcome was achieved with resection of the anomalous articulation. CONCLUSION: Clinicians should consider the possibility that mechanical low back pain may occur from a facet contralateral to a unilateral anomalous lumbosacral articulation, even in a young patient. Although reports of surgical treatment of Bertolotti's syndrome are infrequent, resection of the anomalous articulation provided excellent results in this patient, presumably because of reduced stresses on the symptomatic facet.

Cervical muscle response during whiplash: evidence of a lengthening muscle contraction.

OBJECTIVE: To assess the potential for cervical muscle injury from a rear-end automobile collision. DESIGN: Experimental design in which human subjects were exposed to low-speed rear-end collisions. The influence of independent variable (gender, speed change, muscle group, and motion phase) on dependent variables (kinematic response, muscle onset and muscle activation level) was examined using repeated-measures analysis of variance. BACKGROUND: Injuries to various tissues of the cervical spine have been proposed, yet little attention has been focused on the cervical muscles as a site of injury. METHODS: 42 subjects (21 males, 20-40 yr) were exposed to collisions of 4 and 8 km/h speed change while measuring kinematic response of the head and torso and electromyography of the sternocleidomastoid and cervical paraspinal muscles. RESULTS: Muscle activation occurred earlier in females and in the 8 km/h speed change. Sternocleidomastoid onset preceded paraspinal onset. Muscle activation level varied significantly with speed change, motion phase and muscle group. Initial rearward retraction of the head relative to the torso resulted in lengthening of the activated sternocleidomastoid, consistent with a contraction-induced muscle injury. CONCLUSIONS: The cervical muscles contract rapidly in response to impact and the potential exists for muscle injury due to lengthening contractions. RELEVANCE: The clinician should recognize the role of cervical retraction in the mechanism of whiplash injury and avoid aggressive motion in that plane during diagnosis and treatment. An understanding of whiplash injury mechanisms should improve patient education and preventative measures.

The relationship between clinical and kinematic responses from human subject testing in rear-end automobile collisions.

Recent experiments have produced a linked data set of clinical and kinematic responses for human subjects exposed to controlled low-speed rear-end collisions. The purpose of this paper was to examine this paired data set and determine whether the presence or absence of clinical symptoms could be predicted from the peak linear and angular kinematic response of the head and neck. The data were generated using 42 male and female human subjects seated normally in the front passenger seat of a stationary vehicle struck from behind to produce vehicle speed changes of 4 and 8 km/h. Pre- and post-test clinical examinations documented the presence, severity and duration of whiplash-associated disorders (WAD). Logistic regression and backward elimination of independent variables were used to develop the prediction model. The analysis yielded a 16 parameter model that was significantly related (odds ratio = 21.2; P = 0.0069) to the presence or absence of transient whiplash symptoms. The model correctly predicted symptom presence in 13 of 23 tests (sensitivity 57%) and symptom absence in 49 of 52 tests (specificity 94%) in a population of 75 with a symptom prevalence of 31%. The model's positive predictive value was 81% and its negative predictive value was 83%. Despite statistical significance, the model did not discriminate between the presence and absence of symptoms in all tests, and indicated that factors other than the selected peak kinematic responses influenced symptom production.

[Bilateral intracranial subdural hematoma following lumbar puncture: report of a case]. / Hématome sous-dural intra-crânien bilatéral après ponction lombaire: un cas.

A chronic, bilateral, intra-cranial subdural hematoma was diagnosed in a 28 year old man. A standard diagnostic spinal tap had been performed 6 weeks before. There was no other etiologic factor. Intra-cranial subdural hematoma is a rare complication of either diagnostic, therapeutic, or accidental lumbar puncture. Extensive literature review disclosed the description of 49 other cases, including only 3 cases following a standard diagnostic lumbar puncture. Outcome was fatal in 9 of them. The possibility of an intra-cranial subdural hematoma has to be considered in case of prolonged or unusual headache following a lumbar puncture, even with a headache-free period, knowing the emergency of the surgical therapeutic procedure. The most likely mechanism is subdural venous bleeding induced by the chronic intracranial hypotension due to the persisting lumbar meningeal wound.

Electromyographic analysis of shoulder function during the volleyball serve and spike.

The purpose of this study was to describe the electromyographic (EMG) pattern and relative intensities of 8 shoulder muscles during the volleyball serve and spike in 15 professional or collegiate-level athletes. The EMG analysis was synchronized with high-speed cinematography to discern phases of the spike and serve. During the spike, the anterior deltoid and supraspinatus functioned together to elevate and place the humerus throughout all phases. During cocking the infraspinatus and teres minor acted together to rotate the humerus externally. In acceleration, however, these muscles behaved independently; activity of the teres minor remained high, whereas the activity of the infraspinatus declined. The anterior wall muscles functioned to decelerate the humerus during cocking and acted as internal rotators during acceleration. Muscle activities recorded for the serve followed similar patterns as those seen for the spike, but with lower amplitudes. These data illustrate the complex sequence of shoulder muscle activity necessary to play competitive volleyball.

Clinical response of human subjects to rear-end automobile collisions.

OBJECTIVE: Forty-two persons were exposed to controlled low-speed rear-end automobile collisions to assess the relation between both gender and impact severity and the presence, severity, and duration of whiplash-associated disorders (WAD). Individual measures were also assessed for their potential to predict the onset of WAD. DESIGN: Experimental study subjecting individuals to a speed change of 4 km/h and 8 km/h and utilizing pretest and posttest physical examinations (immediately after and 24 hours after impact) to quantify subjects' clinical response. RESULTS: Approximately 29% and 38% of the subjects exposed to the 4 km/h and 8 km/h speed changes, respectively, experienced WAD symptoms, with cervical symptoms and headaches predominating. Objective clinical deficits consistent with WAD were measured in both men and women subjects at both 4 km/h and 8 km/h. At 4 km/h, the duration of symptoms experienced by women was significantly longer when compared with that in men (p < .05). There were no significant differences in the presence and severity of WAD between men and women at 4 km/h and 8 km/h or in the duration of WAD at 8 km/h. There was also no significant difference in the presence, severity, and duration of WAD between 4 km/h and 8 km/h. No preimpact measures were predictive of WAD. CONCLUSION: The empirical findings in this study contribute to establishing a causal relationship between rear-end collisions and clinical signs and symptoms.

Quantification of lumbar intradiscal deformation during flexion and extension, by mathematical analysis of magnetic resonance imaging pixel intensity profiles.

STUDY DESIGN: A magnetic resonance imaging study of the internal kinematic response of normal lumbar intervertebral discs to non-weight-bearing flexion and extension. OBJECTIVES: To quantify the pattern of magnetic resonance imaging pixel intensity variation across discs, and noninvasively monitor displacement of the nucleus pulposus during sagittal-plane movements. SUMMARY OF BACKGROUND DATA: Invasive techniques used to study intradiscal movements of the nucleus pulposus have suggested that it moves posteriorly during flexion and anteriorly during extension. A noninvasive study based on magnetic resonance images gave similar results for normal young women. Quantification has been problematic, and the invasive procedures may have altered disc dynamics. METHODS: Ten male subjects (age, 21-38 years) with healthy backs were positioned in a magnetic resonance imaging portal with their lumbar spine stabilized in flexion and extension by supporting pads. For each disc, a T2-weighted image was obtained, as was a computer-generated profile of pixel intensities along a horizontal mid-discal transect. Mathematical curve-fitting regression analysis was used to characterize the shape of the intensity profile and to compute the point of maximum pixel intensity. RESULTS: A single equation fitted the profile for all normal discs. The intensity peak shifted posteriorly during flexion, anteriorly during extension. CONCLUSIONS: Automated mathematical modeling of magnetic resonance imaging pixel data can be used to describe the fundamental shape of the pixel intensity profile across a normal lumbar disc, to determine the precise location of the site of maximum pixel intensity, and to measure the movement of this peak with flexion and extension. This technique may be of value in recognizing incipient degenerative changes in lumbar discs.