116 research outputs found
Cardiac arrest and COVID-19: inflammation, angiotensin-converting enzyme 2, and the destabilization of non-significant coronary artery disease-a case report.
The new β-coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) appears to exhibit cardiovascular pathogenicity through use of angiotensin-converting enzyme 2 (ACE2) for cell entry and the development of a major systemic inflammation. Furthermore, cardiovascular comorbidities increase susceptibility to SARS-CoV-2 infection and the development of a severe form of COronaVIrus Disease 2019 (COVID-19).
We describe the case of a COVID-19 patient whose inaugural presentation was a refractory cardiac arrest secondary to the destabilization of known, non-significant coronary artery disease. Patient was supported by venoarterial extracorporeal life support. After 12 h of support, cardiac function remained stable on low vasopressor support but the patient remained in a coma and brainstem death was diagnosed.
Myocardial injury is frequently seen among critically unwell COVID-19 patients and increases the risk of mortality. This case illustrates several potential mechanisms that are thought to drive the cardiac complications seen in COVID-19. We present the potential role of inflammation and ACE2 in the pathophysiology of COVID-19
Electronic Raman scattering and photoluminescence from LaSrMnO exhibiting giant magnetoresistance
Raman and Photoluminescence (PL) experiments on correlated metallic
LaSrMnO have been carried out using different excitation
wavelengths as a function of temperature from 15 K to 300 K. Our data suggest a
Raman mode centered at 1800 cm and a PL band at 2.2 eV. The intensities
of the two peaks decrease with increasing temperature. The Raman mode can be
attributed to a plasmon excitation whose frequency and linewidths are
consistent with the measured resistivities. The PL involves intersite
electronic transitions of the manganese ions.Comment: 10 pages + 4 eps figures, Revtex 3.0, figures available on reques
Instability of metal-insulator transition against thermal cycling in phase separated Cr-doped manganites
We show that metal-insulator transition in Pr0.5Ca0.5Mn1-xCrxO3 (x =
0.015-0.025) is unstable against thermal cycling. Insulator-metal transition
shifts down and low temperature resistivity increases each time when the sample
is cycled between a starting temperature TS and a final temperature TF. The
effect is dramatic lower is x. Insulator-metal transition in x = 0.015 can be
completely destroyed by thermal cycling in absence of magnetic field as well as
under H = 2 T. Magnetic measurements suggest that ferromagnetic phase fraction
decreases with thermal cycling. We suggest that increase in strains in
ferromagnetic- charge ordered interface could be a possible origin of the
observed effect.Comment: 14 pages, 5 figures and 2 tables (revised
A-site Randomness Effect on Structural and Physical Properties of Ba-based Perovskite Manganites
The discovery of novel structural and physical properties in the -site
ordered manganite BaMnO ( = Y and rare earth elements) has
demanded new comprehension about perovskite manganese oxides. In the present
study, the -site disordered form, BaMnO, has been
investigated and compared with both BaMnO and
MnO (: Sr, Ca) in the structures and electromagnetic
properties. BaMnO has a primitive cubic perovskite cell
in the structure and magnetic glassy states are dominant as its ground state,
in contrast to the ordinary disordered MnO (: Sr, Ca).
In Pr-compounds with various degrees of Pr/Ba randomness at the -sites, the
-site disorder gradually suppresses both ferromagnetic and A-type
antiferromagnetic transitions and finally leads to a magnetic glassy state in
PrBaMnO. A peculiar behavior, multi-step magnetization
and resistivity change, has been observed in PrBaMnO.
These properties could be closely related to any spatial heterogeneity caused
by the random distribution of Ba and with much different
ionic radius.Comment: 9 pages, to be published in J. Phys. Soc. Jpn. 73 Aug. (2004
Suppression of charge-ordering and appearance of magnetoresistance in a spin-cluster glass manganite La0.3Ca0.7Mn0.8Cr0.2O3
The magnetic properties of electron-doped manganite La0.3Ca0.7MnO3 and
La0.3Ca0.7Mn0.8Cr0.2O3 polycrystalline samples prepared by sol-gel technique
have been investigated between 5 and 300 K in magnetic fields ranging from 0 to
5 T. The transition at 260 K, attributed to charge ordering in La0.3Ca0.7MnO3,
is completely suppressed in the Cr-substituted sample while the onset of a
magnetic remanence followed by the appearance of a magnetic irreversibility at
lower temperatures is observed in both samples. These features indicate that
ferromagnetic clusters coexist with either an antiferromagnetic phase for
La0.3Ca0.7MnO3 or a spin-cluster glass phase for La0.3Ca0.7Mn0.8Cr0.2O3 at the
lowest temperatures. The exponential temperature dependence of the resistivity
for the Cr-substituted sample is consistent with the small polaron hopping
model for 120 K < T < 300 K, while the data are better described by Mott's
hopping mechanism for T < 120 K. Whereas the parent compound La0.3Ca0.7MnO3 is
known to show no magnetoresistance, a large negative magnetoresistance is
observed in the La0.3Ca0.7Mn0.8Cr0.2O3 sample below 120 K. The appearance of
the CMR is attributed to spin dependent hopping between spin clusters and/or
between ferromagnetic domains
Spin-State Transition and Metal-Insulator Transition in LaEuCoO}
We present a study of the structure, the electric resistivity, the magnetic
susceptibility, and the thermal expansion of LaEuCoO. LaCoO
shows a temperature-induced spin-state transition around 100 K and a
metal-insulator transition around 500 K. Partial substitution of La by
the smaller Eu causes chemical pressure and leads to a drastic increase
of the spin gap from about 190 K in LaCoO to about 2000 K in EuCoO, so
that the spin-state transition is shifted to much higher temperatures. A
combined analysis of thermal expansion and susceptibility gives evidence that
the spin-state transition has to be attributed to a population of an
intermediate-spin state with orbital order for and without orbital
order for larger . In contrast to the spin-state transition, the
metal-insulator transition is shifted only moderately to higher temperatures
with increasing Eu content, showing that the metal-insulator transition occurs
independently from the spin-state distribution of the Co ions. Around
the metal-insulator transition the magnetic susceptibility shows a similar
increase for all and approaches a doping-independent value around 1000 K
indicating that well above the metal-insulator transition the same spin state
is approached for all .Comment: 10 pages, 6 figure
Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide
We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C}
270K and ferromagnetic to canted spin glass state at T_f\leq$ 125K is
observed
Magnetic Phases of Electron-Doped Manganites
We study the anisotropic magnetic structures exhibited by electron-doped
manganites using a model which incorporates the double-exchange between orbital
ly degenerate electrons and the super-exchange between
electrons with realistic values of the Hund's coupling(), the
super-exchange coupling(), and the bandwidth(). We look at the
relative stabilities of the G, C and A type antiferromagnetic ph ases. In
particular we find that the G-phase is stable for low electron doping as seen
in experiments. We find good agreement with the experimentally observed
magnetic phase diagrams of electron-doped manganites
() such as NdSrMnO, PrSrMnO,
and SmCaMnO. We can also explain the experimentally
observed orbital structures of the C a nd A phases.
We also extend our calculation for electron-doped bilayer manganites of the
form RAMnO and predict that the C-phase will be
absent in t hese systems due to their reduced dimensionality.Comment: 7 .ps files included. To appear in Phys. Rev. B (Feb 2001
Transport and structural study of pressure-induced magnetic states in Nd0.55Sr0.45MnO3 and Nd0.5Sr0.5MnO3
Pressure effects on the electron transport and structure of Nd1-xSrxMnO3 (x =
0.45, 0.5) were investigated in the range from ambient to ~6 GPa. In
Nd0.55Sr0.45MnO3, the low-temperature ferromagnetic metallic state is
suppressed and a low temperature insulating state is induced by pressure. In
Nd0.5Sr0.5MnO3, the CE-type antiferromagnetic charge-ordering state is
suppressed by pressure. Under pressure, both samples have a similar electron
transport behavior although their ambient ground states are much different. It
is surmised that pressure induces an A-type antiferromagnetic state at low
temperature in both compounds
Formation of finite antiferromagnetic clusters and the effect of electronic phase separation in Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}
We report the first experimental evidence of a magnetic phase arising due to
the thermal blocking of antiferromagnetic clusters in the weakened charge and
orbital ordered system Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}. The third
order susceptibility (\chi_3) is used to differentiate this transition from a
spin or cluster glass like freezing mechanism. These clusters are found to be
mesoscopic and robust to electronic phase separation which only enriches the
antiphase domain walls with holes at the cost of the bulk, without changing the
size of these clusters. This implies that Al substitution provides sufficient
disorder to quench the length scales of the striped phases.Comment: 4 Post Script Figure
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