Cluster Volume Research Articles

Serial Assessment of Gray Matter Abnormalities after Sport-Related Concussion.

There is an urgent need to characterize the acute physiological effects of sport-related concussion (SRC). We investigated the effects of SRC on gray matter structure and diffusion metrics in collegiate athletes at 1.64 (T1; n = 33), 8.33 (T2; n = 30), and 32.15 days (T3; n = 36) post-concussion, with healthy collegiate contact-sport athletes serving as controls (HA; n = 46). Plasma levels of glial fibrillary acidic protein (GFAP) were assessed in a subset of athletes. We hypothesized that acute SRC would be associated with increased fractional anisotropy (FA), decreased mean diffusivity (MD), and increased GFAP relative to noninjured HA, without acute differences in gray matter volume or cortical thickness. Further, we hypothesized that neither diffusion nor structure would show longitudinal changes across the first month post-SRC. Finally, we hypothesized that gray matter diffusion metrics would correlate with plasma GFAP levels, as indicated by pre-clinical literature. Consistent with our hypothesis, acute SRC was associated with decreased MD in the left pallidum, increased FA in the right amygdala, and a significantly greater number and volume of subject-specific clusters with increased FA compared to HA. No differences in gray matter volume, cortical thickness, or GFAP were observed between groups. There were no longitudinal changes in any measure across the first month post-SRC. Finally, FA in the right amygdala was inversely correlated with GFAP at T2. These results suggest that gray matter diffusion metrics may be useful in determining the physiological effects of SRC.

Cluster Recognition by Delaunay Triangulation of Synaptic Proteins in 3D.

The advent of super-resolution microscopy opens up the opportunity to study biological structures in unprecedented detail. However, revealing quantitative information about the spatial organization of a set of labeled proteins requires sophisticated analysis. This study introduces a novel robust cluster recognition algorithm based on Delaunay triangulation (CRADT), which can handle complex datasets generated by 3D super-resolution microscopy. This algorithm allows determining volume and shape of protein clusters in 3D. The study demonstrates its performance by applying this algorithm on dual-color 3D super-resolved measurements of mouse hippocampal synapses, stained against the presynaptic active zone marker protein Bassoon and the opposing postsynaptic density protein Homer as well as the exo- and endocytosis machinery proteins Synaptobrevin and Clathrin.

Interaction Effects in Assembly of Magnetic Nanoparticles

A specific absorption rate of a dilute assembly of various random clusters of iron oxide nanoparticles in alternating magnetic field has been calculated using Landau–Lifshitz stochastic equation. This approach simultaneously takes into account both the presence of thermal fluctuations of the nanoparticle magnetic moments and magneto-dipole interaction between the nanoparticles of the clusters. It is shown that for usual 3D clusters, the intensity of the magneto-dipole interaction is determined mainly by the cluster packing density η = NpV/Vcl, where Np is the average number of the particles in the cluster, V is the nanoparticle volume, and Vcl is the cluster volume. The area of the low frequency hysteresis loop and the assembly-specific absorption rate have been found to be considerably reduced when the packing density of the clusters increases in the range of 0.005 ≤ η < 0.4. The dependence of the specific absorption rate on the mean nanoparticle diameter is retained with an increase of η, but becomes less pronounced. For fractal clusters of nanoparticles, which arise in biological media, in addition to a considerable reduction of the absorption rate, the absorption maximum is shifted to smaller particle diameters. It is found also that the specific absorption rate of fractal clusters increases appreciably with an increase of the thickness of nonmagnetic shells at the nanoparticle surfaces.

Comparison of C14- and C15-Predomiated AB2 Metal Hydride Alloys for Electrochemical Applications

Herein, we present a comparison of the electrochemical hydrogen-storage characteristics of two state-of-art Laves phase-based metal hydride alloys (Zr21.5Ti12.0V10.0Cr7.5Mn8.1Co8.0Ni32.2Sn0.3Al0.4 vs. Zr25.0Ti6.5V3.9Mn22.2Fe3.8Ni38.0La0.3) prepared by induction melting and hydrogen decrepitation. The relatively high contents of lighter transition metals (V and Cr) in the first composition results in an average electron density below the C14/C15 threshold ( e / a ~ 6.9 ) and produces a C14-predominated structure, while the average electron density of the second composition is above the C14/C15 threshold and results in a C15-predominated structure. From a combination of variations in composition, main phase structure, and degree of homogeneity, the C14-predominated alloy exhibits higher storage capacities (in both the gaseous phase and electrochemical environment), a slower activation, inferior high-rate discharge, and low-temperature performances, and a better cycle stability compared to the C15-predominated alloy. The superiority in high-rate dischargeability in the C15-predominated alloy is mainly due to its larger reactive surface area. Annealing of the C15-predominated alloy eliminates the ZrNi secondary phase completely and changes the composition of the La-containing secondary phase. While the former change sacrifices the synergetic effects, and degrades the hydrogen storage performance, the latter may contribute to the unchanged surface catalytic ability, even with a reduction in total volume of metallic nickel clusters embedded in the activated surface oxide layer. In general, the C14-predominated alloy is more suitable for high-capacity and long cycle life applications, and the C15-predominated alloy can be used in areas requiring easy activation, and better high-rate and low-temperature performances.

Catechol-O-Methyltransferase Val158Met Polymorphism on Striatum Structural Covariance Networks in Alzheimer\u2019s Disease

The catechol-O-methyltransferase enzyme metabolizes dopamine in the prefrontal axis, and its genetic polymorphism (rs4680; Val158Met) is a known determinant of dopamine signaling. In this study, we investigated the possible structural covariance networks that may be modulated by this functional polymorphism in patients with Alzheimer’s disease. Structural covariance networks were constructed by 3D T1 magnetic resonance imaging. The patients were divided into two groups: Met-carriers (n = 91) and Val-homozygotes (n = 101). Seed-based analysis was performed focusing on triple-network models and six striatal networks. Neurobehavioral scores served as the major outcome factors. The role of seed or peak cluster volumes, or a covariance strength showing Met-carriers > Val-homozygotes were tested for the effect on dopamine. Clinically, the Met-carriers had higher mental manipulation and hallucination scores than the Val-homozygotes. The volume-score correlations suggested the significance of the putaminal seed in the Met-carriers and caudate seed in the Val-homozygotes. Only the dorsal-rostral and dorsal-caudal putamen interconnected peak clusters showed covariance strength interactions (Met-carriers > Val-homozygotes), and the peak clusters also correlated with the neurobehavioral scores. Although the triple-network model is important for a diagnosis of Alzheimer’s disease, our results validated the role of the dorsal-putaminal-anchored network by the catechol-O-methyltransferase Val158Met polymorphism in predicting the severity of cognitive and behavior in subjects with Alzheimer’s disease.

IMPACT OF PLASMA GLUCOSE ON THE PATTERN OF BRAIN FDG UPTAKE IN COGNITIVELY NORMAL ELDERLY SUBJECTS

Several studies reported increased blood glucose levels (BGL) to be associated with alterations of regional uptake of F-18-fluorodeoxyglucose (FDG) in the brain that mimic the characteristic pattern of Alzheimer's disease (AD)-related hypometabolism. Aim of the present study was to test this relationship in well characterized normal controls of the Alzheimer's Disease Neuroimaging Initiative (ADNI). The study included all ADNI control subjects with baseline FDG-PET that were cognitively stable for at least 36 months (n=87, 74.2±5.3y, 40 females). Pre-processed FDG-PET data was downloaded and stereotactically normalized to MNI space using SPM8. The mean signal in brain parenchyma was used for intensity scaling. Voxelwise multiple regression was used to test the effect of BGL on scaled FDG uptake, using a cluster-defining voxel-level threshold of p=0.05, uncorrected. Resulting clusters were considered statistically significant if the family-wise error corrected p-value of the cluster was 0.05 or less. BGL ranged between 59 and 149 mg/dl (98±16 mg/dl). There was a significant cluster of negative correlation between scaled FDG uptake and BGL comprising precuneus and bilateral parieto-occipital cortex (cluster volume 123 ml, p=0.020). The cluster did not include the posterior cingulate. Positive correlation was detected in a large cluster of white matter in the centrum semiovale (245 ml, p<0.0005). A piecewise linear broken stick model used to fit mean FDG uptake in the cluster of negative correlation as a function of BGL identified a breaking point at 94 mg/dl. Unexpectedly, the decline of scaled FDG uptake in this cluster was steeper below the breaking point than above. The broken stick provided a better fit of the data than a straight line (Akaike Information Criterion).

The paradox of a long grounding during West Antarctic Ice Sheet retreat in Ross Sea

Marine geological data show that the West Antarctic Ice Sheet (WAIS) advanced to the eastern Ross Sea shelf edge during the Last Glacial Maximum (LGM) and eventually retreated ~1000 km to the current grounding-line position on the inner shelf. During the early deglacial, the WAIS deposited a voluminous stack of overlapping grounding zone wedges (GZWs) on the outer shelf of the Whales Deep Basin. The large sediment volume of the GZW cluster suggests that the grounding-line position of the paleo-Bindschadler Ice Stream was relatively stationary for a significant time interval. We used an upper bound estimate of paleo-sediment flux to investigate the lower bound duration over which the ice stream would have deposited sediment to account for the GZW volume. Our calculations show that the cluster represents more than three millennia of ice-stream sedimentation. This long duration grounding was probably facilitated by rapid GZW growth. The subsequent punctuated large-distance (~200 km) grounding-line retreat may have been a highly non-linear ice sheet response to relatively continuous external forcing such as gradual climate warming or sea-level rise. These findings indicate that reliable predictions of future WAIS retreat may require incorporation of realistic calculations of sediment erosion, transport and deposition.

Updates in computed tomography assessment of emphysema using computed tomography lung analysis

IntroductionComputed tomography (CT) lung analysis is a new CT technique that allows assessment of emphysema in a quantitative pattern to avoid subjective analysis.ObjectiveThe aim of this study was to assess the role of a new CT lung analysis in quantitative assessment of pulmonary emphysema.Patients and methodsTotally, 30 patients with emphysema were included in this study who presented to the Chest Department of Ain Shams University for follow-up. All patients underwent full history taking, clinical examination, spirometry, and body plethysmography, and were then referred to the Radiology Department for noncontrast chest CT followed by lung volume analysis. Four patients among them were followed-up before and after medical volume reduction therapy.ResultsThere was a direct relationship between the CT lung volume, the percentage of low-attenuation area, as well as the total lung capacity measured by body plethysmography. Totally, 12 cases were found to be grade I by the Goddard score, with nine of them found to be GOLD I and three of them found to be GOLD II. Fifteen cases were found to be grade II by the Goddard score, with 12 of them found to be GOLD II and three of them found to be GOLD III/IV. Three cases were found to be grade III by the Goddard score with all of them found to be GOLD III/IV. The main site for distribution of the clusters according to their number was in the left upper lobe, whereas according to the cluster volume the main site was the right upper lobe. CT lung analysis guided the site of injection in four patients who underwent volume reduction therapy.ConclusionCT lung analysis is a new technique that allows quantitative assessment of emphysema, which is important for categorization, follow-up, and treatment strategies. It must be added as a routine study accompanied by spirometric function.

The bound fraction of young star clusters

The residual gas within newly formed star clusters is expelled through stellar feedback on timescales ~ 1 Myr. The subsequent expansion of the cluster results in an unbinding of a fraction of stars before the remaining cluster members can re-virialize and form a surviving cluster. We investigate the bound fraction after gas expulsion as a function of initial cluster mass in stars and gauge the influence of primordial mass segregation, stellar evolution and the tidal field at the solar distance. We also assess the impact of the star-formation efficiency and gas expulsion velocity. We perform N-body simulations using Sverre Aarseth's NBODY7 code, starting with compact clusters in their embedded phase and approximate the gas expulsion by means of an exponentially depleting external gravitational field. We follow the process of re-virialization through detailed monitoring of different Lagrange radii over several Myr, examining initial half-mass radii of 0.1 pc, 0.3 pc and 0.5 pc and initial masses usually ranging from $5\times10^3 M_\odot$ to $5\times10^4 M_\odot$. The adopted star-formation efficiency of 0.33 in the cluster volume results in a distinct sensitivity to the gas expulsion velocity over a wide mass range, while a variation of the star-formation efficiency can make the cluster robust to the rapidly decreasing external potential. We confirm that primordial mass segregation leads to a smaller bound fraction, its influence possibly decreasing with mass. Stellar evolution has a higher impact on lower mass clusters, but heating through dynamical friction could expand the cluster to a similar extent. The examined clusters expand well within their tidal radii and would survive gas expulsion even in a strong tidal field.

Genetic effect of MTHFR C677T polymorphism on the structural covariance network and white-matter integrity in Alzheimer's disease.

The 677 C to T transition in the MTHFR gene is a genetic determinant for hyperhomocysteinemia. We investigated whether this polymorphism modulates gray matter (GM) structural covariance networks independently of white-matter integrity in patients with Alzheimer's disease (AD). GM structural covariance networks were constructed by 3D T1-magnetic resonance imaging and seed-based analysis. The patients were divided into two genotype groups: C homozygotes (n = 73) and T carriers (n = 62). Using diffusion tensor imaging and white-matter parcellation, 11 fiber bundle integrities were compared between the two genotype groups. Cognitive test scores were the major outcome factors. The T carriers had higher homocysteine levels, lower posterior cingulate cortex GM volume, and more clusters in the dorsal medial lobe subsystem showing stronger covariance strength. Both posterior cingulate cortex seed and interconnected peak cluster volumes predicted cognitive test scores, especially in the T carriers. There were no between-group differences in fiber tract diffusion parameters. The MTHFR 677T polymorphism modulates posterior cingulate cortex-anchored structural covariance strength independently of white matter integrities. Hum Brain Mapp 38:3039-3051, 2017. © 2017 The Authors Human Brain Mapping Published Wiley by Periodicals, Inc.

An evaluation of Z-transform algorithms for identifying subject-specific abnormalities in neuroimaging data.

The need for algorithms that capture subject-specific abnormalities (SSA) in neuroimaging data is increasingly recognized across many neuropsychiatric disorders. However, the effects of initial distributional properties (e.g., normal versus non-normally distributed data), sample size, and typical preprocessing steps (spatial normalization, blurring kernel and minimal cluster requirements) on SSA remain poorly understood. The current study evaluated the performance of several commonly used z-transform algorithms [leave-one-out (LOO); independent sample (IDS); Enhanced Z-score Microstructural Assessment of Pathology (EZ-MAP); distribution-corrected z-scores (DisCo-Z); and robust z-scores (ROB-Z)] for identifying SSA using simulated and diffusion tensor imaging data from healthy controls (N=50). Results indicated that all methods (LOO, IDS, EZ-MAP and DisCo-Z) with the exception of the ROB-Z eliminated spurious differences that are present across artificially created groups following a standard z-transform. However, LOO and IDS consistently overestimated the true number of extrema (i.e., SSA) across all sample sizes and distributions. The EZ-MAP and DisCo-Z algorithms more accurately estimated extrema across most distributions and sample sizes, with the exception of skewed distributions. DTI results indicated that registration algorithm (linear versus non-linear) and blurring kernel size differentially affected the number of extrema in positive versus negative tails. Increasing the blurring kernel size increased the number of extrema, although this effect was much more prominent when a minimum cluster volume was applied to the data. In summary, current results highlight the need to statistically compare the frequency of SSA in control samples or to develop appropriate confidence intervals for patient data.

The XMM cluster outskirts project (X‐COP)

Galaxy clusters are thought to grow hierarchically through the continuous merging and accretion of smaller structures across cosmic time. In the local universe, these phenomena are still active in the outer regions of massive clusters (R &gt; R500), where the matter distribution is expected to become clumpy and asymmetric because of the presence of accreting structures. We present the XMM‐Newton cluster outskirts project (X‐COP), which targets the outer regions of a sample of 13 massive clusters (M500 &gt; 3 × 1014M⊙) in the redshift range 0.04–0.1 at uniform depth. The sample was selected based on the signal‐to‐noise ratio in the Planck Sunyaev–Zeldovich (SZ) survey with the aim of combining high‐quality X‐ray and SZ constraints throughout the entire cluster volume. Our observing strategy allows us to reach a sensitivity of 3 × 10− 16 ergs cm− 1 s− 1 arcmin− 2 in the 0.5–2.0 keV range thanks to a good control of systematic uncertainties. The combination of depth and field of view achieved in X‐COP will allow us to pursue the following main goals: (a) measure the distribution of entropy and thermal energy to an unprecedented level of precision; (b) assess the presence of nonthermal pressure support in cluster outskirts; and (c) study the occurrence and mass distribution of infalling gas clumps. We illustrate the capabilities of the program with a pilot study on the cluster Abell 2142.

Changes in dorsolateral prefrontal connectivity after rTMS in treatment-resistant depression: a brain perfusion SPECT study.

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive and safe alternative to electroconvulsive therapy for treatment-resistant depression (TRD). After rTMS, changes in brain SPECT perfusion have been remotely identified within medial temporal limbic areas, while no local effects have been found within the left dorsolateral prefrontal cortex (DLPFC)-i.e. under the coil. Functional changes in connectivity may underlie these remote effects. Interestingly, functional connectivity has been recently investigated using perfusion SPECT, and abnormalities identified in TRD patients. The aim of the present study is to evaluate perfusion and connectivity SPECT changes in TRD patients after rTMS of the left DLPFC. We hypothesize that changes in DLPFC networks may explain remote hypoperfusions found after rTMS. Fifty-eight TRD patients underwent a brain SPECT before and after high-frequency rTMS of the left DLPFC. Whole-brain voxel-based changes in perfusion were evaluated with SPM8, and inter-regional correlation analysis performed to study left DLPFC functional connectivity (p < 0.005, corrected for cluster volume). After rTMS, patients were significantly improved on Beck Depression Inventory score (p < 0.0001). Considering a 50% reduction threshold, 27 patients were identified as responders (47%). After rTMS, perfusion changes were not found locally within the left DLPFC, but remotely within the bilateral temporal lobes, including limbic areas. Inter-regional correlation SPECT analysis brings out a decrease of connectivity between the left DLPFC and both the cingulate/medial frontal cortex and bilateral medial temporal limbic areas, in relation with the clinical response. rTMS of DLPFC in TRD patients leads to remote temporal hypoperfusions in relation with changes in functional connectivity between the DLPFC and the default mode network, especially including medial temporal limbic areas.

Genetic effect of interleukin-1 beta (C-511T) polymorphism on the structural covariance network and white matter integrity in Alzheimer\u2019s disease

BackgroundInflammatory processes play a pivotal role in the degenerative process of Alzheimer’s disease. In humans, a biallelic (C/T) polymorphism in the promoter region (position-511) (rs16944) of the interleukin-1 beta gene has been significantly associated with differences in the secretory capacity of interleukin-1 beta. In this study, we investigated whether this functional polymorphism mediates the brain networks in patients with Alzheimer’s disease.MethodsWe enrolled a total of 135 patients with Alzheimer’s disease (65 males, 70 females), and investigated their gray matter structural covariance networks using 3D T1 magnetic resonance imaging and their white matter macro-structural integrities using fractional anisotropy. The patients were classified into two genotype groups: C-carriers (n = 108) and TT-carriers (n = 27), and the structural covariance networks were constructed using seed-based analysis focusing on the default mode network medial temporal or dorsal medial subsystem, salience network and executive control network. Neurobehavioral scores were used as the major outcome factors for clinical correlations.ResultsThere were no differences between the two genotype groups in the cognitive test scores, seed, or peak cluster volumes and white matter fractional anisotropy. The covariance strength showing C-carriers > TT-carriers was the entorhinal-cingulum axis. There were two peak clusters (Brodmann 6 and 10) in the salience network and four peak clusters (superior prefrontal, precentral, fusiform, and temporal) in the executive control network that showed C-carriers < TT-carriers in covariance strength. The salience network and executive control network peak clusters in the TT group and the default mode network peak clusters in the C-carriers strongly predicted the cognitive test scores.ConclusionsInterleukin-1 beta C-511 T polymorphism modulates the structural covariance strength on the anterior brain network and entorhinal-interconnected network which were independent of the white matter tract integrity. Depending on the specific C-511 T genotype, different network clusters could predict the cognitive tests.

Direct observation of active material interactions in flowable electrodes using X-ray tomography.

Understanding electrical percolation and charging mechanisms in electrochemically active biphasic flowable electrodes is critical for enabling scalable deionization (desalination) and energy storage. Flowable electrodes are dynamic material systems which store charge (remove ions) and have the ability to flow. This flow process can induce structural changes in the underlying material arrangement and result in transient and non-uniform material properties. Carbon-based suspensions are opaque, multi-phase, and three dimensional, and thus prior characterization of the structural properties has been limited to indirect methods (electrochemical and rheology). Herein, a range of mixed electronic and ionically conducting suspensions are evaluated to determine their static structure, function, and properties, utilizing synchrotron radiation X-ray tomographic microscopy (SRXTM). The high brilliance of the synchrotron light enables deconvolution of the liquid and solid phases. Reconstruction of the solid phase reveals agglomeration cluster volumes between 10 μm3 and 103μm3 (1 pL) for low loaded samples (5 wt% carbon). The largest agglomeration cluster in the low loaded sample (5 wt%) occupied only 3% of the reconstructed volume whereas samples loaded with 10 wt% activated carbon demonstrated electrically connected clusters that occupied 22% of the imaged region. The highly loaded samples (20 wt%) demonstrated clusters of the order of a microliter, which accounted for 63-85% of the imaged region. These results demonstrate a capability for discerning the structural properties of biphasic systems utilizing SRXTM techniques, and show that discontinuity in the carbon particle networks induces decreased material utilization in low-loaded flowable electrodes.

Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and a prolonged depletion of residual scCO2. In this study, pore-scale scCO2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9MPa and 40°C by injecting scCO2 into the sandstone-analogue pore network initially saturated by water without dissolved CO2 (dsCO2). During the experiments, time-lapse images of dye intensity, reflecting water pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO2 dissolution and phase equilibrium occurs when scCO2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO2 dissolution at phase interfaces and diffusion of dsCO2 at the pore scale (10–100µm) observed after scCO2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO2 at narrow pore throats.

Effective viscosity of nanofluids — A modified Krieger–Dougherty model based on particle size distribution (PSD) analysis

Nanofluids (colloidal suspensions of nano-sized metallic and non-metallic particles in conventional cooling liquids) are well known for their potential to enhance the thermal transport. Excessive attempts have been made to utilize these nanofluids in heat transfer applications and energy conversion systems, etc. Effective viscosity of nanofluids is a pivotal parameter in determining the flow and heat transfer performance of nanofluids. The prime aim of this work is to develop a new model for effective viscosity of nanofluids. The influences of aggregation and interfacial layer formation have been incorporated into the Krieger–Dougherty (K–D) equation to predict the effective viscosity of nanofluids. This is accomplished by characterizing the clusters based on particle size distribution (PSD) analysis. Furthermore, attention has been paid to showcase the effects of cluster volume fraction, particle diameter and surfactants on effective viscosity of nanofluids. The predicted results are in good agreement with a wide variety of experimental data from literature consisting of different combinations of nanoparticles and basefluid. The accuracy and ease of application of the newly proposed model make it more interesting and useful for practical engineers in design and development of heat transfer systems using nanofluids.

Ion-irradiation induced clustering in W-Re-Ta, W-Re and W-Ta alloys: An atom probe tomography and nanoindentation study

In tungsten plasma-facing fusion reactor components, Ta is the third most abundant element formed by transmutation (after Re and Os), yet little is known about the behaviour of W-Ta alloys under irradiation and any effects Ta might have on Re clustering in W-Re-Ta alloys. In this study, W−4.5 at.%Ta, W−2 at.%Re−1 at.%Ta and W−2 at.%Re alloys were exposed to 2 MeV W+ ions to a fluence of 2.64 × 1015 ions cm−2 at temperatures of 573 and 773 K. Atom probe tomography and nanoindentation were used to characterise the chemical and physical properties of the irradiation-induced clusters and the mechanical properties of the irradiated layer. In the W-Ta alloy, no evidence of irradiation-induced clustering was found. In the W−Re−Ta alloy, at both irradiation temperatures studied the presence of Ta reduced the W-Re cluster number density and volume fraction compared to that in the W-Re alloy; however it did not alter cluster composition as the Ta was rejected from the clusters. The reduced cluster density in the W-Re-Ta alloys was associated with a smaller degree of irradiation hardening than in the W-Re alloys. Possible mechanisms by which Ta hinders cluster development are discussed.

Inhomogeneous State of the Bi2Te3 Doped with Manganese

Basing on electron spin resonance (ESR) data for Bi2Te3 doped by Mn ions we argue that this compound can be inhomogeneous and consists of two components with the different structures. Its main phase Bi 2−xMn xTe 3 is intertwined with the microscopical inclusions of MnBi phase. The integral volume of these intermetal clusters is less than 1 % but nevertheless they exert the serious impact on the dynamic magnetic properties of the entire system. These inclusions are ferromagnetic with the Curie temperature of 630 K, while the main bulk phase Bi 2−xMn xTe 3 has x= 0.05 orders at Tc= 10 K (qualitatively this twophase picture is valid not only for this given x). Below this temperature two ferromagnetic phases coexist. Since the integral spontaneous polarization in MnBi phase is averaged out due to its random orientations in different clusters the time-reversal symmetry of Bi 2Te 3 doped by Mn ions is violated only at the low-temperature ferromagnetic transition.

Turbulence and vorticity in Galaxy clusters generated by structure formation

Turbulence is a key ingredient for the evolution of the intracluster medium, whose properties can be predicted with high-resolution numerical simulations. We present initial results on the generation of solenoidal and compressive turbulence in the intracluster medium during the formation of a small-size cluster using highly resolved, non-radiative cosmological simulations, with a refined monitoring in time. In this first of a series of papers, we closely look at one simulated cluster whose formation was distinguished by a merger around z ∼ 0.3. We separate laminar gas motions, turbulence and shocks with dedicated filtering strategies and distinguish the solenoidal and compressive components of the gas flows using Hodge–Helmholtz decomposition. Solenoidal turbulence dominates the dissipation of turbulent motions (∼95 per cent) in the central cluster volume at all epochs. The dissipation via compressive modes is found to be more important (∼30 per cent of the total) only at large radii (≥0.5rvir) and close to merger events. We show that enstrophy (vorticity squared) is good proxy of solenoidal turbulence. All terms ruling the evolution of enstrophy (i.e. baroclinic, compressive, stretching and advective terms) are found to be significant, but in amounts that vary with time and location. Two important trends for the growth of enstrophy in our simulation are identified: first, enstrophy is continuously accreted into the cluster from the outside, and most of that accreted enstrophy is generated near the outer accretion shocks by baroclinic and compressive processes. Secondly, in the cluster interior vortex, stretching is dominant, although the other terms also contribute substantially.