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Search Results: 1 - 10 of 167633 matches for " E. Springate "
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Effect of Glutathione Depletion on Ifosfamide Nephrotoxicity in Rats
Sudha Garimella-Krovi,James E. Springate
International Journal of Biomedical Science , 2008,
Abstract: Kidney injury is an important side effect of the chemotherapeutic agent ifosfamide in humans. Previous studies have shown that treatment with ifosfamide reduces kidney glutathione and that the toxicity of ifosfamide is enhanced in glutathione-depleted renal tubule cells in vitro. In this study, we examined the effect of glutathione depletion on ifosfamide nephrotoxicity in vivo using rats treated with the glutathione-depleting agent buthionine sulfoximine. Animals received 80 mg/kg ifosfamide intraperitoneally daily for three days with or without buthionine sulfoximine in drinking water. Buthionine sulfoximine produced a significant fall in renal glutathione content but did not affect kidney function. Ifosfamide-treated rats developedlow-grade glucosuria, phosphaturia and proteinuria that worsened with concomitant buthionine sulfoximine therapy. These findings indicate that glutathione depletion exacerbates ifosfamide nephrotoxicity in rats and suggest that pharmacological methods for replenishing intracellular glutathione may be effective in ameliorating ifosfamide-induced renal injury.
Tracking primary thermalization events in graphene with photoemission at extreme timescales
I. Gierz,F. Calegari,S. Aeschlimann,M. Chavez Cervantes,C. Cacho,R. T. Chapman,E. Springate,S. Link,U. Starke,C. R. Ast A. Cavalleri
Physics , 2015, DOI: 10.1103/PhysRevLett.115.086803
Abstract: Direct and inverse Auger scattering are amongst the primary processes that mediate the thermalization of hot carriers in semiconductors. These two processes involve the annihilation or generation of an electron-hole pair by exchanging energy with a third carrier, which is either accelerated or decelerated. Inverse Auger scattering is generally suppressed, as the decelerated carriers must have excess energies higher than the band gap itself. In graphene, which is gapless, inverse Auger scattering is instead predicted to be dominant at the earliest time delays. Here, $<8$ femtosecond extreme-ultraviolet pulses are used to detect this imbalance, tracking both the number of excited electrons and their kinetic energy with time- and angle-resolved photoemission spectroscopy. Over a time window of approximately 25 fs after absorption of the pump pulse, we observe an increase in conduction band carrier density and a simultaneous decrease of the average carrier kinetic energy, revealing that relaxation is in fact dominated by inverse Auger scattering. Measurements of carrier scattering at extreme timescales by photoemission will serve as a guide to ultrafast control of electronic properties in solids for PetaHertz electronics.
A Re-Analysis of the Cochrane Library Data: The Dangers of Unobserved Heterogeneity in Meta-Analyses
Evangelos Kontopantelis, David A. Springate, David Reeves
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0069930
Abstract: Background Heterogeneity has a key role in meta-analysis methods and can greatly affect conclusions. However, true levels of heterogeneity are unknown and often researchers assume homogeneity. We aim to: a) investigate the prevalence of unobserved heterogeneity and the validity of the assumption of homogeneity; b) assess the performance of various meta-analysis methods; c) apply the findings to published meta-analyses. Methods and Findings We accessed 57,397 meta-analyses, available in the Cochrane Library in August 2012. Using simulated data we assessed the performance of various meta-analysis methods in different scenarios. The prevalence of a zero heterogeneity estimate in the simulated scenarios was compared with that in the Cochrane data, to estimate the degree of unobserved heterogeneity in the latter. We re-analysed all meta-analyses using all methods and assessed the sensitivity of the statistical conclusions. Levels of unobserved heterogeneity in the Cochrane data appeared to be high, especially for small meta-analyses. A bootstrapped version of the DerSimonian-Laird approach performed best in both detecting heterogeneity and in returning more accurate overall effect estimates. Re-analysing all meta-analyses with this new method we found that in cases where heterogeneity had originally been detected but ignored, 17–20% of the statistical conclusions changed. Rates were much lower where the original analysis did not detect heterogeneity or took it into account, between 1% and 3%. Conclusions When evidence for heterogeneity is lacking, standard practice is to assume homogeneity and apply a simpler fixed-effect meta-analysis. We find that assuming homogeneity often results in a misleading analysis, since heterogeneity is very likely present but undetected. Our new method represents a small improvement but the problem largely remains, especially for very small meta-analyses. One solution is to test the sensitivity of the meta-analysis conclusions to assumed moderate and large degrees of heterogeneity. Equally, whenever heterogeneity is detected, it should not be ignored.
Evidence of reduced surface electron-phonon scattering in the conduction band of Bi_{2}Se_{3} by non-equilibrium ARPES
A. Crepaldi,F. Cilento,B. Ressel,C. Cacho,J. C. Johannsen,M. Zacchigna,H. Berger,Ph. Bugnon,C. Grazioli,I. C. E. Turcu,E. Springate,K. Kern,M. Grioni,F. Parmigiani
Physics , 2013, DOI: 10.1103/PhysRevB.88.121404
Abstract: The nature of the Dirac quasiparticles in topological insulators calls for a direct investigation of the electron-phonon scattering at the \emph{surface}. By comparing time-resolved ARPES measurements of the TI Bi_{2}Se_{3} with different probing depths we show that the relaxation dynamics of the electronic temperature of the conduction band is much slower at the surface than in the bulk. This observation suggests that surface phonons are less effective in cooling the electron gas in the conduction band.
Possible observation of parametrically amplified coherent phasons in K0.3MoO3 using time-resolved extreme-ultraviolet ARPES
H. Y. Liu,I. Gierz,J. C. Petersen,S. Kaiser,A. Simoncig,A. L. Cavalieri,C. Cacho,I. C. E. Turcu,E. Springate,F. Frassetto,L. Poletto,S. S. Dhesi,Z. -A. Xu,T. Cuk,R. Merlin,A. Cavalleri
Physics , 2012, DOI: 10.1103/PhysRevB.88.045104
Abstract: We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) in the Extreme Ultraviolet (EUV) to measure the time- and momentum-dependent electronic structure of photo-excited K0.3MoO3. Prompt depletion of the Charge Density Wave (CDW) condensate launches coherent oscillations of the amplitude mode, observed as a 1.7-THz-frequency modulation of the bonding band position. In contrast, the anti-bonding band oscillates at about half this frequency. We attribute these oscillations to coherent excitation of phasons via parametric amplification of phase fluctuations.
Probing the structure and dynamics of molecular clusters using rotational wavepackets
Gediminas Galinis,Cephise Cacho,Richard T. Chapman,Andrew M. Ellis,Marius Lewerenz,Luis G. Mendoza Luna,Russell S. Minns,Mirjana Mladenovic,Arnaud Rouzée,Emma Springate,I. C. Edmond Turcu,Mark J. Watkins,Klaus von Haeften
Physics , 2014, DOI: 10.1103/PhysRevLett.113.043004
Abstract: The chemical and physical properties of molecular clusters can heavily depend on their size, which makes them very attractive for the design of new materials with tailored properties. Deriving the structure and dynamics of clusters is therefore of major interest in science. Weakly bound clusters can be studied using conventional spectroscopic techniques, but the number of lines observed is often too small for a comprehensive structural analysis. Impulsive alignment generates rotational wavepackets, which provides simultaneous information on structure and dynamics, as has been demonstrated successfully for isolated molecules. Here, we apply this technique for the firsttime to clusters comprising of a molecule and a single helium atom. By forcing the population of high rotational levels in intense laser fields we demonstrate the generation of rich rotational line spectra for this system, establishing the highly delocalised structure and the coherence of rotational wavepacket propagation. Our findings enable studies of clusters of different sizes and complexity as well as incipient superfluidity effects using wavepacket methods.
Momentum resolved spin dynamics of bulk and surface excited states in the topological insulator $\mathrm{Bi_{2}Se_{3}}$
C. Cacho,A. Crepaldi,M. Battiato,J. Braun,F. Cilento,M. Zacchigna,M. C. Richter,O. Heckmann,E. Springate,Y. Liu,S. S. Dhesi,H. Berger,Ph. Bugnon,K. Held,M. Grioni,H. Ebert,K. Hricovini,J. Minár,F. Parmigiani
Physics , 2014, DOI: 10.1103/PhysRevLett.114.097401
Abstract: The prospective of optically inducing a spin polarized current for spintronic devices has generated a vast interest in the out-of-equilibrium electronic and spin structure of topological insulators (TIs). In this Letter we prove that only by measuring the spin intensity signal over several order of magnitude in spin, time and angle resolved photoemission spectroscopy (STAR-PES) experiments is it possible to comprehensively describe the optically excited electronic states in TIs materials. The experiments performed on $\mathrm{Bi_{2}Se_{3}}$ reveal the existence of a Surface-Resonance-State in the 2nd bulk band gap interpreted on the basis of fully relativistic ab-initio spin resolved photoemission calculations. Remarkably, the spin dependent relaxation of the hot carriers is well reproduced by a spin dynamics model considering two non-interacting electronic systems, derived from the excited surface and bulk states, with different electronic temperatures.
ClinicalCodes: An Online Clinical Codes Repository to Improve the Validity and Reproducibility of Research Using Electronic Medical Records
David A. Springate, Evangelos Kontopantelis, Darren M. Ashcroft, Ivan Olier, Rosa Parisi, Edmore Chamapiwa, David Reeves
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0099825
Abstract: Lists of clinical codes are the foundation for research undertaken using electronic medical records (EMRs). If clinical code lists are not available, reviewers are unable to determine the validity of research, full study replication is impossible, researchers are unable to make effective comparisons between studies, and the construction of new code lists is subject to much duplication of effort. Despite this, the publication of clinical codes is rarely if ever a requirement for obtaining grants, validating protocols, or publishing research. In a representative sample of 450 EMR primary research articles indexed on PubMed, we found that only 19 (5.1%) were accompanied by a full set of published clinical codes and 32 (8.6%) stated that code lists were available on request. To help address these problems, we have built an online repository where researchers using EMRs can upload and download lists of clinical codes. The repository will enable clinical researchers to better validate EMR studies, build on previous code lists and compare disease definitions across studies. It will also assist health informaticians in replicating database studies, tracking changes in disease definitions or clinical coding practice through time and sharing clinical code information across platforms and data sources as research objects.
Function-Valued Traits in Evolution
Pantelis Z. Hadjipantelis,Nick S. Jones,John Moriarty,David A. Springate,Christopher G. Knight
Quantitative Biology , 2012,
Abstract: Many biological characteristics of evolutionary interest are not scalar variables but continuous functions. Given a dataset of function-valued traits generated by evolution, we develop a practical statistical approach to infer ancestral function-valued traits, and estimate the generative evolutionary process. We do this by combining dimension reduction and phylogenetic Gaussian process regression, a nonparametric procedure which explicitly accounts for known phylogenetic relationships. We test the methods' performance on simulated function-valued data generated from a stochastic evolutionary model. The methods are applied assuming that only the phylogeny and the function-valued traits of taxa at its tips are known. Our method is robust and applicable to a wide range of function-valued data, and also offers a phylogenetically aware method for estimating the autocorrelation of function-valued traits.
Ancestral Inference from Functional Data: Statistical Methods and Numerical Examples
Pantelis Z. Hadjipantelis,Nick S. Jones,John Moriarty,David Springate,Christopher G. Knight
Quantitative Biology , 2012,
Abstract: Many biological characteristics of evolutionary interest are not scalar variables but continuous functions. Here we use phylogenetic Gaussian process regression to model the evolution of simulated function-valued traits. Given function-valued data only from the tips of an evolutionary tree and utilising independent principal component analysis (IPCA) as a method for dimension reduction, we construct distributional estimates of ancestral function-valued traits, and estimate parameters describing their evolutionary dynamics.
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