Matthias Schabel - Academia.edu (original) (raw)
Uploads
Papers by Matthias Schabel
Physical Review B, 1998
... theory the main difference between these two is that the chains mediate electron transport al... more ... theory the main difference between these two is that the chains mediate electron transport along the c axis in Y123, leading to strong dispersion in this direc-tion, while the chain geometry in Y124 frustrates conduc-tion, with consequent suppression of dispersion.911 Never ...
Physical Review B, 1998
... theory the main difference between these two is that the chains mediate electron transport al... more ... theory the main difference between these two is that the chains mediate electron transport along the c axis in Y123, leading to strong dispersion in this direc-tion, while the chain geometry in Y124 frustrates conduc-tion, with consequent suppression of dispersion.911 Never ...
We report ARPES spectra both above and below Tc in underdoped superconducting thin films of Bi 22... more We report ARPES spectra both above and below Tc in underdoped superconducting thin films of Bi 2212 grown by molecular beam epitaxy. Underdoping (as controlled by oxygen content and/or Dy doping) is found to introduce a new feature in the electronic structure, an anisotropic gap which persists well above T_c. As in the superconducting state, the gap is measurable near (π,0) and is zero within experimental resolution at 0.4(π,π).
We performed angle-resolved photoemission experiments on NiS_2-xSex single crystals on samples wi... more We performed angle-resolved photoemission experiments on NiS_2-xSex single crystals on samples with various values of x. This system shows an insulator-to-metal transition with increasing x. In the vicinity of this transition, we observed a narrow band, characteristic of many-body effects, which develops near the Fermi level. This finding is consistent with predictions of recent theoretical calculations of the Hubbard model solved in the limit of infinite dimensions. Samples with x ≈ 0.5 also exhibit metal-insulator transitions with temperature. We studied the temperature dependence of a x=0.45 sample, which is metallic for T<35K and insulating above this temperature. We observed two discontinuous changes as we raised the temperature through 35K: a sudden shift of the narrow near-EF feature away from the Fermi level and an abrupt decrease in intensity of this feature at the transition temperature.
Physical Review B, 1997
Polarization-dependent angle-resolved photoemission studies of untwinned single crystals of YBa2C... more Polarization-dependent angle-resolved photoemission studies of untwinned single crystals of YBa2Cu3O6.95 (Y123) reveal modifications of the near-Fermi-edge spectral weight which are indicative of an anisotropic superconducting gap. The measured magnitude of the leading edge shift increases monotonically from the Gamma-S line toward the zone boundary, reaching a maximum value of approximately 25 meV, similar to the behavior seen in Bi2Sr2CaCu2O8+delta (Bi2212).
Journal of Immunological Methods, 2009
A storm of inflammatory cytokines is released during treatment with pro-inflammatory cytokines, s... more A storm of inflammatory cytokines is released during treatment with pro-inflammatory cytokines, such as interleukin-2 (IL-2), closely approximating changes initially observed during sepsis. These signals induce profound changes in neurologic function and cognition. Little is known about the mechanisms involved. We evaluated a number of experimental methods to quantify changes in brain blood vessel integrity in a well-characterized IL-2 treatment mouse model. Measurement of wet versus dry weight and direct measurement of small molecule accumulation (e.g. [ 3 H]-H 2 O, sodium fluorescein) were not sensitive or reliable enough to detect small changes in mouse brain vascular permeability. Estimation of brain water content using proton density magnetic resonance imaging (MRI) measurements using a 7 T mouse MRI system was sensitive to 1-2% changes in brain water content, but was difficult to reproduce in replicate experiments. Successful techniques included use of immunohistochemistry using specific endothelial markers to identify vasodilation in carefully matched regions of brain parenchyma and dynamic contrast enhanced (DCE) MRI. Both techniques indicated that IL-2 treatment induced vasodilation of the brain blood vessels. DCE MRI further showed a 2-fold increase in the brain blood vessel permeability to gadolinium in IL-2 treated mice compared to controls. Both immunohistochemistry and DCE MRI data suggested that IL-2 induced toxicity in the brain results from vasodilation of the brain blood vessels and increased microvascular permeability, resulting in perivascular edema. These experimental techniques provide us with the tools to further characterize the mechanism responsible for cytokine-induced neuropsychiatric toxicity.
Pharmaceutical Research, 2005
Purpose. To investigate the pharmacokinetics, long-term tissue retention of Gd(III) ions, and mag... more Purpose. To investigate the pharmacokinetics, long-term tissue retention of Gd(III) ions, and magnetic resonance imaging (MRI) contrast enhancement of extracellular biodegradable macromolecular Gd(III) complexes, (Gd-DTPA)-cystamine copolymers (GDCC), of different molecular weights. Methods. The pharmacokinetics of blood clearance and long-term Gd(III) retention of GDCC were investigated in Sprague-Dawley rats. Pharmacokinetic parameters were calculated by using a two-compartment model. The blood pool contrast enhancement of GDCC was evaluated in Sprague-Dawley rats on a Siemens Trio 3T MR scanner. Gd-(DTPA-BMA) was used as a control. Results. The α phase half-life of Gd-(DTPA-BMA) and GDCC with molecular weights of 18,000 (GDCC-18) and 60,000 Da (GDCC-60) was 0.48 ± 0.16 min, 1.08 ± 0.24 min, and 1.74 ± 0.57 min, and the β phase half-life was 21.2 ± 5.5 min, 26.5 ± 5.9 min, and 53.7 ± 15.9 min, respectively. GDCC had minimal long-term Gd tissue retention comparable to that of Gd-(DTPA-BMA). GDCC resulted in more significant contrast enhancement in the blood pool than Gd-(DTPA-BMA). Conclusions. GDCC provides a prolonged blood pool retention time for effective MRI contrast enhancement and then clears rapidly with minimal accumulation of Gd (III) ions. It is promising for further development as a blood pool MRI contrast agent.
Journal of Climate, 2003
Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of th... more Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of the Microwave Sounding Unit (MSU) temperature record show little or no warming, while surface temperature trends based on in situ observations show a pronounced warming of ϳ0.2 K decade Ϫ1 . This discrepancy between trends at the surface and in the upper atmosphere has been a source of significant debate. Model predictions of amplification of warming with height in the troposphere are clearly inconsistent with the available observations, leading some researchers to question the adequacy of their representation of the water vapor greenhouse feedback. A reanalysis of the MSU channel 2 dataset, with the objective of providing a second independent source of these data, is described in this paper. Results presented herein show a global trend of 0.097 Ϯ 0.020 K decade Ϫ1 , generally agreeing with the work of Prabhakara et al. but in disagreement with the MSU analysis of Christy and Spencer, which shows significantly less (ϳ0.09 K decade Ϫ1 ) warming. Differences in the various methodologies are discussed and it is demonstrated that the principal source of these discrepancies is in the treatment of errors due to variations in the temperature of the MSU hot calibration target.
Time series of total atmospheric column water vapor as determined from SSM/I measurements and tro... more Time series of total atmospheric column water vapor as determined from SSM/I measurements and tropospheric air temperatures from a complete reanalysis of the MSU channel 2 record are analyzed on various spatial and temporal scales in order to elucidate corresponding correlations between these two climate change proxies. Strong correlations between spatial averages over complete circulation systems are observed on time scales ranging from seasonal through interannual to decadal, with the vapor/temperature scaling largely consistent with that expected from the Clausius-Clapeyron thermodynamic relation. As the temperature-water vapor feedback is a critical element in warming amplification by greenhouse gas heat trapping, with much of the variability in global circulation models climate response estimates arising from different vapor parameterizations, application of a hierarchy of correlation and fingerprinting techniques utilizing these two highly stable and precise observational data sets should enable significant improvements in comparative validation of competing model treatments of the T-V feedback dynamics.
Channel 2 of the 9 Microwave Sounding Units (MSUs) flown on NOAA polar orbiting platforms provide... more Channel 2 of the 9 Microwave Sounding Units (MSUs) flown on NOAA polar orbiting platforms provides a 23year time series of middle-tropospheric temperature. These measurements may be of sufficient quality for climate studies if intersatellite calibration offsets and drifts can be accurately characterized and removed. One of the most important and difficult to characterize sources of long-term drift in the data is due to the evolution of the local observing time due to slow changes in the orbital parameters of each NOAA platform, which can alias diurnal temperature changes into the long-term time series. To account for this effect, we have constructed monthly diurnal climatologies of MSU Channel 2 brightness temperature using the hourly output of a general circulation model as input for a microwave radiative transfer model. We report the results of this calculation, and validate the result by comparing with MSU observations.
Journal of Climate, 2003
Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of th... more Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of the Microwave Sounding Unit (MSU) temperature record show little or no warming, while surface temperature trends based on in situ observations show a pronounced warming of 0.2 K decade-1. This discrepancy between trends at the surface and in the upper atmosphere has been a source of significant debate. Model predictions of amplification of warming with height in the troposphere are clearly inconsistent with the available observations, leading some researchers to question the adequacy of their representation of the water vapor greenhouse feedback. A reanalysis of the MSU channel 2 dataset, with the objective of providing a second independent source of these data, is described in this paper. Results presented herein show a global trend of 0.097 ± 0.020 K decade-1, generally agreeing with the work of Prabhakara et al. but in disagreement with the MSU analysis of Christy and Spencer, which shows significantly less (0.09 K decade-1) warming. Differences in the various methodologies are discussed and it is demonstrated that the principal source of these discrepancies is in the treatment of errors due to variations in the temperature of the MSU hot calibration target.
Nature, 1998
The 17-year lower-tropospheric temperature record derived from the satellite Microwave Sounding U... more The 17-year lower-tropospheric temperature record derived from the satellite Microwave Sounding Unit (MSU) shows a global cooling trend, from 1979 to 1995, of -0.05K per decade at an altitude of about 3.5km (refs 4, 5). Air temperatures measured at the Earth&amp;#39;s surface, in contrast, have risen by approximately +0.13K per decade over the same period,. The two temperature records are
Physical Review B, 1991
Using the Keating valence-force-field model with large periodic supercells, we analyze the struct... more Using the Keating valence-force-field model with large periodic supercells, we analyze the structural relaxations of pseudobinary III-V and II-VI semiconductor alloys. We quantitatively predict the dependence of bond lengths and second-neighbor distances on alloy composition, and show that the multimodal distributions of second-neighbor distances may be explained in terms of a simple set of local geometries. Intrinsic alloy broadening of bond-length distributions is also calculated and compared with experimentally measured values.
Physical Review B, 1998
... theory the main difference between these two is that the chains mediate electron transport al... more ... theory the main difference between these two is that the chains mediate electron transport along the c axis in Y123, leading to strong dispersion in this direc-tion, while the chain geometry in Y124 frustrates conduc-tion, with consequent suppression of dispersion.911 Never ...
Physical Review B, 1998
... theory the main difference between these two is that the chains mediate electron transport al... more ... theory the main difference between these two is that the chains mediate electron transport along the c axis in Y123, leading to strong dispersion in this direc-tion, while the chain geometry in Y124 frustrates conduc-tion, with consequent suppression of dispersion.911 Never ...
We report ARPES spectra both above and below Tc in underdoped superconducting thin films of Bi 22... more We report ARPES spectra both above and below Tc in underdoped superconducting thin films of Bi 2212 grown by molecular beam epitaxy. Underdoping (as controlled by oxygen content and/or Dy doping) is found to introduce a new feature in the electronic structure, an anisotropic gap which persists well above T_c. As in the superconducting state, the gap is measurable near (π,0) and is zero within experimental resolution at 0.4(π,π).
We performed angle-resolved photoemission experiments on NiS_2-xSex single crystals on samples wi... more We performed angle-resolved photoemission experiments on NiS_2-xSex single crystals on samples with various values of x. This system shows an insulator-to-metal transition with increasing x. In the vicinity of this transition, we observed a narrow band, characteristic of many-body effects, which develops near the Fermi level. This finding is consistent with predictions of recent theoretical calculations of the Hubbard model solved in the limit of infinite dimensions. Samples with x ≈ 0.5 also exhibit metal-insulator transitions with temperature. We studied the temperature dependence of a x=0.45 sample, which is metallic for T<35K and insulating above this temperature. We observed two discontinuous changes as we raised the temperature through 35K: a sudden shift of the narrow near-EF feature away from the Fermi level and an abrupt decrease in intensity of this feature at the transition temperature.
Physical Review B, 1997
Polarization-dependent angle-resolved photoemission studies of untwinned single crystals of YBa2C... more Polarization-dependent angle-resolved photoemission studies of untwinned single crystals of YBa2Cu3O6.95 (Y123) reveal modifications of the near-Fermi-edge spectral weight which are indicative of an anisotropic superconducting gap. The measured magnitude of the leading edge shift increases monotonically from the Gamma-S line toward the zone boundary, reaching a maximum value of approximately 25 meV, similar to the behavior seen in Bi2Sr2CaCu2O8+delta (Bi2212).
Journal of Immunological Methods, 2009
A storm of inflammatory cytokines is released during treatment with pro-inflammatory cytokines, s... more A storm of inflammatory cytokines is released during treatment with pro-inflammatory cytokines, such as interleukin-2 (IL-2), closely approximating changes initially observed during sepsis. These signals induce profound changes in neurologic function and cognition. Little is known about the mechanisms involved. We evaluated a number of experimental methods to quantify changes in brain blood vessel integrity in a well-characterized IL-2 treatment mouse model. Measurement of wet versus dry weight and direct measurement of small molecule accumulation (e.g. [ 3 H]-H 2 O, sodium fluorescein) were not sensitive or reliable enough to detect small changes in mouse brain vascular permeability. Estimation of brain water content using proton density magnetic resonance imaging (MRI) measurements using a 7 T mouse MRI system was sensitive to 1-2% changes in brain water content, but was difficult to reproduce in replicate experiments. Successful techniques included use of immunohistochemistry using specific endothelial markers to identify vasodilation in carefully matched regions of brain parenchyma and dynamic contrast enhanced (DCE) MRI. Both techniques indicated that IL-2 treatment induced vasodilation of the brain blood vessels. DCE MRI further showed a 2-fold increase in the brain blood vessel permeability to gadolinium in IL-2 treated mice compared to controls. Both immunohistochemistry and DCE MRI data suggested that IL-2 induced toxicity in the brain results from vasodilation of the brain blood vessels and increased microvascular permeability, resulting in perivascular edema. These experimental techniques provide us with the tools to further characterize the mechanism responsible for cytokine-induced neuropsychiatric toxicity.
Pharmaceutical Research, 2005
Purpose. To investigate the pharmacokinetics, long-term tissue retention of Gd(III) ions, and mag... more Purpose. To investigate the pharmacokinetics, long-term tissue retention of Gd(III) ions, and magnetic resonance imaging (MRI) contrast enhancement of extracellular biodegradable macromolecular Gd(III) complexes, (Gd-DTPA)-cystamine copolymers (GDCC), of different molecular weights. Methods. The pharmacokinetics of blood clearance and long-term Gd(III) retention of GDCC were investigated in Sprague-Dawley rats. Pharmacokinetic parameters were calculated by using a two-compartment model. The blood pool contrast enhancement of GDCC was evaluated in Sprague-Dawley rats on a Siemens Trio 3T MR scanner. Gd-(DTPA-BMA) was used as a control. Results. The α phase half-life of Gd-(DTPA-BMA) and GDCC with molecular weights of 18,000 (GDCC-18) and 60,000 Da (GDCC-60) was 0.48 ± 0.16 min, 1.08 ± 0.24 min, and 1.74 ± 0.57 min, and the β phase half-life was 21.2 ± 5.5 min, 26.5 ± 5.9 min, and 53.7 ± 15.9 min, respectively. GDCC had minimal long-term Gd tissue retention comparable to that of Gd-(DTPA-BMA). GDCC resulted in more significant contrast enhancement in the blood pool than Gd-(DTPA-BMA). Conclusions. GDCC provides a prolonged blood pool retention time for effective MRI contrast enhancement and then clears rapidly with minimal accumulation of Gd (III) ions. It is promising for further development as a blood pool MRI contrast agent.
Journal of Climate, 2003
Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of th... more Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of the Microwave Sounding Unit (MSU) temperature record show little or no warming, while surface temperature trends based on in situ observations show a pronounced warming of ϳ0.2 K decade Ϫ1 . This discrepancy between trends at the surface and in the upper atmosphere has been a source of significant debate. Model predictions of amplification of warming with height in the troposphere are clearly inconsistent with the available observations, leading some researchers to question the adequacy of their representation of the water vapor greenhouse feedback. A reanalysis of the MSU channel 2 dataset, with the objective of providing a second independent source of these data, is described in this paper. Results presented herein show a global trend of 0.097 Ϯ 0.020 K decade Ϫ1 , generally agreeing with the work of Prabhakara et al. but in disagreement with the MSU analysis of Christy and Spencer, which shows significantly less (ϳ0.09 K decade Ϫ1 ) warming. Differences in the various methodologies are discussed and it is demonstrated that the principal source of these discrepancies is in the treatment of errors due to variations in the temperature of the MSU hot calibration target.
Time series of total atmospheric column water vapor as determined from SSM/I measurements and tro... more Time series of total atmospheric column water vapor as determined from SSM/I measurements and tropospheric air temperatures from a complete reanalysis of the MSU channel 2 record are analyzed on various spatial and temporal scales in order to elucidate corresponding correlations between these two climate change proxies. Strong correlations between spatial averages over complete circulation systems are observed on time scales ranging from seasonal through interannual to decadal, with the vapor/temperature scaling largely consistent with that expected from the Clausius-Clapeyron thermodynamic relation. As the temperature-water vapor feedback is a critical element in warming amplification by greenhouse gas heat trapping, with much of the variability in global circulation models climate response estimates arising from different vapor parameterizations, application of a hierarchy of correlation and fingerprinting techniques utilizing these two highly stable and precise observational data sets should enable significant improvements in comparative validation of competing model treatments of the T-V feedback dynamics.
Channel 2 of the 9 Microwave Sounding Units (MSUs) flown on NOAA polar orbiting platforms provide... more Channel 2 of the 9 Microwave Sounding Units (MSUs) flown on NOAA polar orbiting platforms provides a 23year time series of middle-tropospheric temperature. These measurements may be of sufficient quality for climate studies if intersatellite calibration offsets and drifts can be accurately characterized and removed. One of the most important and difficult to characterize sources of long-term drift in the data is due to the evolution of the local observing time due to slow changes in the orbital parameters of each NOAA platform, which can alias diurnal temperature changes into the long-term time series. To account for this effect, we have constructed monthly diurnal climatologies of MSU Channel 2 brightness temperature using the hourly output of a general circulation model as input for a microwave radiative transfer model. We report the results of this calculation, and validate the result by comparing with MSU observations.
Journal of Climate, 2003
Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of th... more Over the period from 1979 to 2001, tropospheric trends derived from a widely cited analysis of the Microwave Sounding Unit (MSU) temperature record show little or no warming, while surface temperature trends based on in situ observations show a pronounced warming of 0.2 K decade-1. This discrepancy between trends at the surface and in the upper atmosphere has been a source of significant debate. Model predictions of amplification of warming with height in the troposphere are clearly inconsistent with the available observations, leading some researchers to question the adequacy of their representation of the water vapor greenhouse feedback. A reanalysis of the MSU channel 2 dataset, with the objective of providing a second independent source of these data, is described in this paper. Results presented herein show a global trend of 0.097 ± 0.020 K decade-1, generally agreeing with the work of Prabhakara et al. but in disagreement with the MSU analysis of Christy and Spencer, which shows significantly less (0.09 K decade-1) warming. Differences in the various methodologies are discussed and it is demonstrated that the principal source of these discrepancies is in the treatment of errors due to variations in the temperature of the MSU hot calibration target.
Nature, 1998
The 17-year lower-tropospheric temperature record derived from the satellite Microwave Sounding U... more The 17-year lower-tropospheric temperature record derived from the satellite Microwave Sounding Unit (MSU) shows a global cooling trend, from 1979 to 1995, of -0.05K per decade at an altitude of about 3.5km (refs 4, 5). Air temperatures measured at the Earth&amp;#39;s surface, in contrast, have risen by approximately +0.13K per decade over the same period,. The two temperature records are
Physical Review B, 1991
Using the Keating valence-force-field model with large periodic supercells, we analyze the struct... more Using the Keating valence-force-field model with large periodic supercells, we analyze the structural relaxations of pseudobinary III-V and II-VI semiconductor alloys. We quantitatively predict the dependence of bond lengths and second-neighbor distances on alloy composition, and show that the multimodal distributions of second-neighbor distances may be explained in terms of a simple set of local geometries. Intrinsic alloy broadening of bond-length distributions is also calculated and compared with experimentally measured values.