333 research outputs found
Effect of Growth Hormone (hGH) Replacement Therapy on Physical Work Capacity and Cardiac and Pulmonary Function in Patients with hGH Deficiency Acquired in Adulthood.
The effects of 6 months of replacement therapy with recombinant human GH (hGH) on physical work capacity and cardiac structure and function were investigated in 20 patients with hGH deficiency of adult onset in a double blind, placebo-controlled trial. The GH dose of 12.5 micrograms/kg BW was self-administered daily sc. Oxygen consumption (VO2), CO2 production, and ventilatory volumes were measured during exercise on a bicycle spiroergometer. M-Mode echocardiography was performed using standard techniques. The VO2 max data, expressed per kg BW (mL/min.kg BW) showed a significant increase from 23.2 +/- 2.4 to 30.0 +/- 2.3 (P < 0.01) in the hGH-treated group, whereas the VO2 max data, expressed per lean body mass (milliliters per min/kg lean body mass) did not change significantly in either group. Maximal O2 pulse (milliliters per beat) increased significantly from 15.2 +/- 5.6 to 19.6 +/- 3.3 mL/beat (P < 0.01), but remained constant in the placebo group. The maximal power output (watts +/- SE) increased significantly (P < 0.01) from 192.5 +/- 13.5 to 227.5 +/- 11.5 in the hGH-treated group, but remained constant in the placebo group. Cardiac structure (left ventricular posterior wall, interventricular septum thickness, left ventricular mass, left ventricular end-systolic dimension, and left ventricular end-diastolic dimension) as well as echocardiographically assessed cardiac function did not change significantly after 6 months of treatment in either group. We conclude that hGH replacement in hGH-deficient adults improves oxygen uptake and exercise capacity. These improvements in pulmonary parameters might be due to an increase in respiratory muscle strength and partly to the changes in muscle volume per se observed during hGH replacement therapy. Furthermore, an increased cardiac output might contribute to the improvement in exercise performance during hGH treatment. According to our data, hGH replacement therapy leads to an improvement of exercise capacity and maximal oxygen uptake, but has no significant effect on cardiac structure
Magnetic order and spin dynamics across a ferromagnetic quantum critical point: SR investigations of YbNi(PAs)
In the quasi-1D heavy-fermion system YbNi(PAs) the
presence of a ferromagnetic (FM) quantum critical point (QCP) at with unconventional quantum critical exponents in the thermodynamic
properties has been recently reported. Here, we present muon-spin relaxation
(SR) experiments on polycrystals of this series to study the magnetic
order and the low energy 4-electronic spin dynamics across the FM QCP. The
zero field SR measurements on pure YbNi(P proved static long
range magnetic order and suggested a strongly reduced ordered Yb moment of
about 0.04. With increasing As substitution the ordered moment is
reduced by half at and to less than 0.005 at . The
dynamic behavior in the SR response show that magnetism remains
homogeneous upon As substitution, without evidence for disorder effect. In the
paramagnetic state across the FM QCP the dynamic muon-spin relaxation rate
follows 1/ with . The critical fluctuations are very slow and are even becoming slower
when approaching the QCP.Comment: 6 pages, 4 figure
Biodegradable and compostable alternatives to conventional plastics
This article is available open access through the publisher’s website at the link below. Copyright @ 2009 The Royal Society.Packaging waste forms a significant part of municipal solid waste and has caused increasing environmental concerns, resulting in a strengthening of various regulations aimed at reducing the amounts generated. Among other materials, a wide range of oil-based polymers is currently used in packaging applications. These are virtually all non-biodegradable, and some are difficult to recycle or reuse due to being complex composites having varying levels of contamination. Recently, significant progress has been made in the development of biodegradable plastics, largely from renewable natural resources, to produce biodegradable materials with similar functionality to that of oil-based polymers. The expansion in these bio-based materials has several potential benefits for greenhouse gas balances and other environmental impacts over whole life cycles and in the use of renewable, rather than finite resources. It is intended that use of biodegradable materials will contribute to sustainability and reduction in the environmental impact associated with disposal of oil-based polymers.
The diversity of biodegradable materials and their varying properties makes it difficult to make simple, generic assessments such as biodegradable products are all ‘good’ or petrochemical-based products are all ‘bad’. This paper discusses the potential impacts of biodegradable packaging materials and their waste management, particularly via composting. It presents the key issues that inform judgements of the benefits these materials have in relation to conventional, petrochemical-based counterparts. Specific examples are given from new research on biodegradability in simulated ‘home’ composting systems. It is the view of the authors that biodegradable packaging materials are most suitable for single-use disposable applications where the post-consumer waste can be locally composted.EPSR
Giant spin canting in the S = 1/2 antiferromagnetic chain [CuPM(NO3)2(H2O)2]n observed by 13C-NMR
We present a combined experimental and theoretical study on copper pyrimidine
dinitrate [CuPM(NO3)2(H2O)2]n, a one-dimensional S = 1/2 antiferromagnet with
alternating local symmetry. From the local susceptibility measured by NMR at
the three inequivalent carbon sites in the pyrimidine molecule we deduce a
giant spin canting, i.e., an additional staggered magnetization perpendicular
to the applied external field at low temperatures. The magnitude of the
transverse magnetization, the spin canting of 52 degrees at 10 K and 9.3 T and
its temperature dependence are in excellent agreement with exact
diagonalization calculations.Comment: 5 pages, 6 Postscript figure
Dzyaloshinsky-Moriya Spin Canting in the LTT Phase of La2-x-yEuySrxCuO4
The Cu spin magnetism in La2-x-yEuySrxCuO4 (x<=0.17; y<=0.2) has been studied
by means of magnetization measurements up to 14 T. Our results clearly show
that in the antiferromagnetic phase Dzyaloshinsky-Moriya (DM)superexchange
causes Cu spin canting not only in the LTO phase but also in the LTLO and LTT
phases. In La1.8Eu0.2CuO4 the canted DM-moment is about 50% larger than in pure
La2CuO4 which we attribute to the larger octahedral tilt angle. We also find
clear evidence that the size of the DM-moment does not change significantly at
the structural transition at T_LT from LTO to LTLO and LTT. The most important
change induced by the transition is a significant reduction of the magnetic
coupling between the CuO2 planes. As a consequence, the spin-flip transition of
the canted Cu spins which is observed in the LTO phase for magnetic field
perpendicular to the CuO2 planes disappears in the LTT phase. The shape of the
magnetization curves changes from the well known spin-flip type to a
weak-ferromagnet type. However, no spontaneous weak ferromagnetism is observed
even at very low temperatures, which seems to indicate that the interlayer
decoupling in our samples is not perfect. Nonetheless, a small fraction (<15%)
of the DM-moments can be remanently magnetized throughout the entire
antiferromagnetically ordered LTT/LTLO phase, i.e. for T<T_LT and x<0.02. It
appears that the remanent DM-moment is perpendicular to the CuO2 planes. For
magnetic field parallel to the CuO2 planes we find that the critical field of
the spin-flop transition decreases in the LTLO phase, which might indicate a
competition between different in-plane anisotropies. To study the Cu spin
magnetism in La2-x-yEuySrxCuO4, a careful analysis of the Van Vleck
paramagnetism of the Eu3+ ions was performed.Comment: 22 pages, 27 figure
Quantum critical dynamics of a S = 1/2 antiferromagnetic Heisenberg chain studied by 13C-NMR spectroscopy
We present a 13C-NMR study of the magnetic field driven transition to
complete polarization of the S=1/2 antiferromagnetic Heisenberg chain system
copper pyrazine dinitrate Cu(C_4H_4N_2)(NO_3)_2 (CuPzN). The static local
magnetization as well as the low-frequency spin dynamics, probed via the
nuclear spin-lattice relaxation rate 1/T_1, were explored from the low to the
high field limit and at temperatures from the quantum regime (k_B T << J) up to
the classical regime (k_B T >> J). The experimental data show very good
agreement with quantum Monte Carlo calculations over the complete range of
parameters investigated. Close to the critical field, as derived from static
experiments, a pronounced maximum in 1/T_1 is found which we interpret as the
finite-temperature manifestation of a diverging density of zero-energy magnetic
excitations at the field-driven quantum critical point.Comment: 5 pages, 4 figure
Electronic structure of the molecule based magnet Cu PM(NO3)2 (H2O)2
We present density functional calculations on the molecule based S=1/2
antiferromagnetic chain compound Cu PM(NO3)2 (H2O)2; PM = pyrimidine. The
properties of the ferro- and antiferromagnetic state are investigated at the
level of the local density approximation and with the hybrid functional B3LYP.
Spin density maps illustrate the exchange path via the pyrimidine molecule
which mediates the magnetism in the one-dimensional chain. The computed
exchange coupling is antiferromagnetic and in reasonable agreement with the
experiment. It is suggested that the antiferromagnetic coupling is due to the
possibility of stronger delocalization of the charges on the nitrogen atoms,
compared to the ferromagnetic case. In addition, computed isotropic and
anisotropic hyperfine interaction parameters are compared with recent NMR
experiments
Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCoF
We report high-frequency/high-field electron spin resonance (ESR) and
high-field magnetization studies on single crystals of the bond-disordered
pyrochlore NaCaCoF. Frequency- and temperature-dependent ESR
investigations above the freezing temperature K reveal the
coexistence of two distinct magnetic phases. A cooperative paramagnetic phase,
evidenced by a gapless excitation mode, is found as well as a spin-glass phase
developing below 20 K which is associated with a gapped low-energy excitation.
Effective -factors close to 2 are obtained for both modes in line with
pulsed high-field magnetization measurements which show an unsaturated
isotropic behavior up to 58 T at 2 K. In order to describe the field-dependent
magnetization in high magnetic fields, we propose an empirical model accounting
for highly anisotropic ionic -tensors expected for this material and taking
into account the strongly competing interactions between the spins which lead
to a frustrated ground state. As a detailed quantitative relation between
effective -factors as determined from ESR and the local -tensors obtained
by neutron scattering [Ross et al., Phys. Rev. B 93, 014433 (2016)] is still
sought after, our work motivates further theoretical investigations of the
low-energy excitations in bond-disordered pyrochlores.Comment: 9 pages, 6 figure
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