2,277 research outputs found
Mechanical properties of La-based bulk amorphous alloy and composites
Influence of different microstructure of La-based fully amorphous samples and its composites on the impact fracture energy were investigated and discussed. Results showed improvement in fracture energy of glassy metals with the presence intermetallic phases, but deteriorated in the presence of dendrite phases and high volume % of crystalline phases.Singapore-MIT Alliance (SMA
Patient and health system delays in the diagnosis and treatment of new and retreatment pulmonary tuberculosis cases in Malawi
BACKGROUND: Tuberculosis (TB) control remains a challenge in Malawi despite the National TB Control Program since 1984. This study aimed at measuring patient and health system delays and identifying factors associated with these delays. METHODS: A cross-sectional survey of 588 pulmonary TB patients was conducted in three TB centres in Blantyre, Lilongwe, and Mzuzu, between July and December 2011 using a semi-structured questionnaire. Patient delay was defined as the time interval between the onset of TB symptom(s) (a common symptom being coughing) to the first visit to any health provider. Health system delay was the interval from the first care-seeking visit at any health provider to the initiation of anti-tuberculosis treatment. Participants were invited to participate in the study during intensive phase of treatment. The characteristics associated with patient and health system delays were analyzed. RESULTS: The median patient delay was 14 days for both new and retreatment TB cases (interquartile range [IQR] 14 – 28 and 7 – 21, respectively). The median health system delay was 59 days (IQR 26 – 108) for new and 40.5 days (IQR 21–90) for retreatment cases. Factors associated with longer patient delay in new cases included primary education (adjusted odds ratio [AOR] 2.2, 95% CI 1.3 – 3.9) and knowledge that more than three weeks of coughing is a sign of TB (AOR 1.9, 1.1 – 3.3). In retreatment cases, distance >10 Km (AOR 3.3, 1.1 – 9.6) and knowledge that more than three weeks of coughing is a sign of TB (AOR 3.7, 1.3 – 10.7; p < 0.05) were significant factors. Making the first visit to a health centre (OR 1.9, 0.9 – 3.8) or a drug store/ traditional healer (OR 5.1, 1.1 – 21.7) in new TB cases were associated with a longer health system delay (p < 0.05) while smear negative (OR 6.4, 1.5 – 28.3), and smear unknown or not done (OR 6.1, 1.3 – 26.9) among retreatment cases were associated with a longer health system delay (p < 0.05). CONCLUSIONS: Effective management and new diagnostic techniques are needed especially among retreatment cases. It is also needed to address geographic barriers to accessing care and increasing TB awareness in the community
The Next Generation Virgo cluster Survey. V. modelling the dynamics of M87 with the Made-to-Measure method
We study the dynamics of the giant elliptical galaxy M87 from the central to
the outermost regions with the made-to-measure (M2M) method. We use a new
catalogue of 922 globular cluster line-of- sight velocities extending to a
projected radius of 180 kpc (equivalent to 25 M87 effective radii), and SAURON
integral field unit data within the central 2.4 kpc. 263 globular clusters,
mainly located beyond 40 kpc, are newly observed by the Next Generation Virgo
Survey (NGVS). For the M2M modelling, the gravitational potential is taken as a
combination of a luminous matter potential with a constant stellar
mass-to-light ratio and a dark matter potential modelled as a logarithmic
potential. Our best dynamical model returns a stellar mass-to-light ratio in
the I band of M/LI = 6.0(+ -0.3) M_sun/L_sun with a dark matter potential scale
velocity of 591(+ -50) km/s and scale radius of 42(+ -10) kpc. We determine the
total mass of M87 within 180 kpc to be (1.5 + - 0.2) 10^13 M_sun. The mass
within 40 kpc is smaller than previous estimates determined using globular
cluster kinematics that did not extend beyond 45 kpc. With our new globular
cluster velocities at much larger radii, we see that globular clusters around
40 kpc show an anomalously large velocity dispersion which affected previous
results. The mass we derived is in good agreement with that inferred from ROSAT
X-ray observation out to 180 kpc. Within 30 kpc our mass is also consistent
with that inferred from Chandra and XMM-Newton X-ray observations, while within
120 kpc it is about 20% smaller. The model velocity dispersion anisotropy beta
parameter for the globular clusters in M87 is small, varying from -0.2 at the
centre to 0.2 at 40 kpc, and gradually decreasing to zero at 120 kpc.Comment: 20 pages, 16 figures, Accepted by Ap
SVM-RFE Based Feature Selection and Taguchi Parameters Optimization for Multiclass SVM Classifier
Recently, support vector machine (SVM) has excellent performance on classification and prediction and is widely used on disease diagnosis or medical assistance. However, SVM only functions well on two-group classification problems. This study combines feature selection and SVM recursive feature elimination (SVM-RFE) to investigate the classification accuracy of multiclass problems for Dermatology and Zoo databases. Dermatology dataset contains 33 feature variables, 1 class variable, and 366 testing instances; and the Zoo dataset contains 16 feature variables, 1 class variable, and 101 testing instances. The feature variables in the two datasets were sorted in descending order by explanatory power, and different feature sets were selected by SVM-RFE to explore classification accuracy. Meanwhile, Taguchi method was jointly combined with SVM classifier in order to optimize parameters C and Îł to increase classification accuracy for multiclass classification. The experimental results show that the classification accuracy can be more than 95% after SVM-RFE feature selection and Taguchi parameter optimization for Dermatology and Zoo databases
Electrical Switching of the Edge Current Chirality in Quantum Anomalous Hall Insulators
A quantum anomalous Hall (QAH) insulator is a topological state of matter, in
which the interior is insulating but electrical current flows along the edges
of the sample, in either clockwise (right-handed) or counter-clockwise
(left-handed) direction dictated by the spontaneous magnetization orientation.
Such chiral edge current (CEC) eliminates any backscattering, giving rise to
quantized Hall resistance and zero longitudinal resistance. In this work, we
fabricate mesoscopic QAH sandwich (i.e. magnetic topological insulator
(TI)/TI/magnetic TI) Hall bar devices and succeed in switching the CEC
chirality in QAH insulators through spin-orbit torque (SOT) by applying a
current pulse and suitably controlled gate voltage. The well-quantized QAH
states with opposite CEC chiralities are demonstrated through four- and
three-terminal measurements before and after SOT switching. Our theoretical
calculations show that the SOT that enables the magnetization switching can be
generated by both bulk and surface carriers in QAH insulators, in good
agreement with experimental observations. Current pulse-induced switching of
the CEC chirality in QAH insulators will not only advance our knowledge in the
interplay between magnetism and topological states but also expedite easy and
instantaneous manipulation of the QAH state in proof-of-concept
energy-efficient electronic and spintronic devices as well as quantum
information applications.Comment: 24 pages, 5 figures, comments are welcom
Even-Odd Layer-Dependent Anomalous Hall Effect in Topological Magnet MnBi2Te4 Thin Films
A central theme in condensed matter physics is to create and understand the
exotic states of matter by incorporating magnetism into topological materials.
One prime example is the quantum anomalous Hall (QAH) state. Recently, MnBi2Te4
has been demonstrated to be an intrinsic magnetic topological insulator and the
QAH effect was observed in exfoliated MnBi2Te4 flakes. Here, we used molecular
beam epitaxy (MBE) to grow MnBi2Te4 films with thickness down to 1 septuple
layer (SL) and performed thickness-dependent transport measurements. We
observed a non-square hysteresis loop in the antiferromagnetic state for films
with thickness greater than 2 SL. The hysteresis loop can be separated into two
AH components. Through careful analysis, we demonstrated that one AH component
with the larger coercive field is from the dominant MnBi2Te4 phase, while the
other AH component with the smaller coercive field is from the minor Mn-doped
Bi2Te3 phase in the samples. The extracted AH component of the MnBi2Te4 phase
shows a clear even-odd layer-dependent behavior, a signature of
antiferromagnetic thin films. Our studies reveal insights on how to optimize
the MBE growth conditions to improve the quality of MnBi2Te4 films, in which
the QAH and other exotic states are predicted.Comment: 23 pages, 4 figures, comments are welcom
Transmembrane Domain Interactions and Residue Proline 378 Are Essential for Proper Structure, Especially Disulfide Bond Formation, in the Human Vitamin K-Dependent Îł-Glutamyl Carboxylase â€
We used recombinant techniques to create a two-chain form (residues 1–345 and residues 346–758) of the vitamin K-dependent γ-glutamyl carboxylase, a glycoprotein located in the endoplasmic reticulum containing five transmembrane domains. The two-chain carboxylase had carboxylase and epoxidase activities similar to those of one-chain carboxylase. In addition, it had normal affinity for the propeptide of factor IX. We employed this molecule to investigate formation of the one disulfide bond in carboxylase, the transmembrane structure of carboxylase, and the potential interactions among the carboxylase’s transmembrane domains. Our results indicate that the two peptides of the two-chain carboxylase are joined by a disulfide bond. Proline 378 is important for the structure necessary for disulfide formation. Results with the P378L carboxylase indicate that noncovalent bonds maintain the two-chain structure even when the disulfide bond is disrupted. As we had previously proposed, the fifth transmembrane domain of carboxylase is the last and only transmembrane domain in the C-terminal peptide of the two-chain carboxylase. We show that the noncovalent association between the two chains of carboxylase involves an interaction between the fifth transmembrane domain and the second transmembrane domain. Results of a homology model of transmembrane domains 2 and 5 suggest that not only do these two domains associate but that transmembrane domain 2 may interact with another transmembrane domain. This latter interaction may be mediated at least in part by a motif of glycine residues in the second transmembrane domain
Directed evolution and predictive modelling of galactose oxidase towards bulky benzylic and unactivated secondary alcohols
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Global metabolic analyses identify key differences in metabolite levels between polymyxin-susceptible and polymyxin-resistant Acinetobacter baumannii
Multidrug-resistant Acinetobacter baumannii presents a global medical crisis and polymyxins are used as the last-line therapy. This study aimed to identify metabolic differences between polymyxin-susceptible and polymyxin-resistant A. baumannii using untargeted metabolomics. The metabolome of each A. baumannii strain was measured using liquid chromatography-mass spectrometry. Multivariate and univariate statistics and pathway analyses were employed to elucidate metabolic differences between the polymyxin-susceptible and -resistant A. baumannii strains. Significant differences were identified between the metabolic profiles of the polymyxin-susceptible and -resistant A. baumannii strains. The lipopolysaccharide (LPS) deficient, polymyxin-resistant 19606R showed perturbation in specific amino acid and carbohydrate metabolites, particularly pentose phosphate pathway (PPP) and tricarboxylic acid (TCA) cycle intermediates. Levels of nucleotides were lower in the LPS-deficient 19606R. Furthermore, 19606R exhibited a shift in its glycerophospholipid profile towards increased abundance of short-chain lipids compared to the parent polymyxin-susceptible ATCC 19606. In contrast, in a pair of clinical isolates 03–149.1 (polymyxin-susceptible) and 03–149.2 (polymyxin-resistant, due to modification of lipid A), minor metabolic differences were identified. Notably, peptidoglycan biosynthesis metabolites were significantly depleted in both of the aforementioned polymyxin-resistant strains. This is the first comparative untargeted metabolomics study to show substantial differences in the metabolic profiles of the polymyxin-susceptible and -resistant A. baumannii
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