818 research outputs found
Rotation of a spheroid in a simple shear at small Reynolds number
We derive an effective equation of motion for the orientational dynamics of a
neutrally buoyant spheroid suspended in a simple shear flow, valid for
arbitrary particle aspect ratios and to linear order in the shear Reynolds
number. We show how inertial effects lift the degeneracy of the Jeffery orbits
and determine the stabilities of the log-rolling and tumbling orbits at
infinitesimal shear Reynolds numbers. For prolate spheroids we find stable
tumbling in the shear plane, log-rolling is unstable. For oblate particles, by
contrast, log-rolling is stable and tumbling is unstable provided that the
aspect ratio is larger than a critical value. When the aspect ratio is smaller
than this value tumbling turns stable, and an unstable limit cycle is born.Comment: 25 pages, 5 figure
Effect of ACTH and CRH on Plasma Levels of Cortisol and Prostaglandin F(2α )Metabolite in Cycling Gilts and Castrated Boars
The present study was designed to evaluate the effects of synthetic ACTH (1–24, tetracosactid) and porcine CRH on the plasma levels of cortisol and PGF(2α )metabolite in cycling gilts (n = 3) and castrated boars (n = 3). The experiments were designed as crossover studies for each gender separately. Each animal received, during three consecutive days; 1) ACTH (Synacthen(® )Depot) at a dose of 10 μg/kg body weight in 5 ml physiological saline, 2) porcine CRH at a dose 0.6 μg/kg body weight in 5 ml physiological saline or 3) physiological saline (5 ml). The test substances were administered via an indwelling jugular cannula in randomized order according to a Latin square. The administration of ACTH to cycling gilts resulted in concomitant elevations of cortisol and PGF(2α )metabolite with peak levels reached at 70.0 ± 10.0 and 33.3 ± 6.7 min, respectively. Similarly, the administration of ACTH to castrated boars resulted in concomitant elevation of cortisol and PGF(2α )metabolite with peak levels reached at 60.0 ± 0.0 and 20.0 ± 0.0 min, respectively. Cortisol peaked at 20 min after administration of CRH in both cycling gilts and castrated boars with maximum levels of 149.3 ± 16.5 nmol/1 and 138.3 ± 10.1 nmol/1, respectively. It can be concluded that administration of synthetic ACTH (tetracosactid) to pigs caused a concomitant elevation of cortisol and PGF(2α )metabolite levels in both cycling gilts as well as castrated boars. The administration of CRH to pigs resulted in an elevation of cortisol levels in both cycling gilts and castrated boars. Conversely, PGF(2α )metabolite levels were not influenced by the administration of CRH either in cycling gilts or in castrated boars
Meissner effect in honeycomb arrays of multi-walled carbon nanotubes
We report Meissner effect for type-II superconductors with a maximum Tc of 19
K, which is the highest value among those in new-carbon related
superconductors, found in the honeycomb arrays of multi-walled CNTs (MWNTs).
Drastic reduction of ferromagnetic catalyst and efficient growth of MWNTs by
deoxidization of catalyst make the finding possible. The weak magnetic
anisotropy, superconductive coherence length (- 7 nm), and disappearance of the
Meissner effect after dissolving array structure indicate that the graphite
structure of an MWNT and those intertube coupling in the honeycomb array are
dominant factors for the mechanism.Comment: 6 page
The role of inertia for the rotation of a nearly spherical particle in a general linear flow
We analyse the angular dynamics of a neutrally buoyant nearly spherical
particle immersed in a steady general linear flow. The hydrodynamic torque
acting on the particle is obtained by means of a reciprocal theorem, regular
perturbation theory exploiting the small eccentricity of the nearly spherical
particle, and assuming that inertial effects are small, but finite.Comment: 7 pages, 1 figur
Impact of Postovulatory Food Deprivation on the Ova Transport, Hormonal Profiles and Metabolic Changes in Sows
The effect of food deprivation on ova transport, hormonal profiles and metabolic changes was studied in 20 crossbred multiparous sows during their second oestrus after weaning. To determine the time of ovulation, transrectal ultrasonographic examination was performed. The sows were divided into 2 groups, one control group (C-group), which was fed according to Swedish standards, and one experimental group (E-group). The E-group sows were deprived of food from the first morning meal after ovulation until slaughter. Blood samples were collected every second hour from about 12 h before expected ovulation in the second oestrus after weaning until slaughter and were analysed for progesterone, prostaglandin F2α-metabolite, insulin, glucose, free fatty acids and triglycerides. All sows were slaughtered approximately 48 h after ovulation and the genital tract was recovered. The isthmic part of the oviduct was divided into 3 equally long segments and flushed separately with phosphate buffered saline (PBS). Uterine horns were also flushed with PBS. A significantly greater number of ova were found in the first and second part of the isthmus in the E-group (p = 0.05) while in the C-group most of the ova were found in the third part of the isthmus or the uterus (p = 0.01). The level of prostaglandin F2α-metabolite was significantly higher in the E-group compared with the C-group. The concentration of progesterone increased in both groups after ovulation but there were no significant differences between the groups. The other blood parameters showed that the food-deprived sows were in a catabolic state. The 48 h period of fasting results, directly or indirectly in an delayed ova transport, which may be due to a delayed relaxation in the smooth circular muscle layer of the isthmus
Temporal and spatial variations in freshwater 14C reservoir effects: Lake Myvatn, Northern Iceland
Lake Mývatn is an interior highland lake in northern Iceland that forms a unique ecosystem of international scientific importance and is surrounded by a landscape rich in archaeological and palaeoenvironmental sites. A significant Freshwater 14C Reservoir Effect (FRE) has been identified in carbon from the lake at some Norse (c.870-1000 AD) archaeological sites in the wider region (Mývatnssveit). Previous AMS measurements indicated this FRE was ~1500-1900 14C years. Here we present the results of a study using stable isotope and 14C measurements to quantify the Mývatn FRE for both the Norse and modern periods. This work has identified a temporally variable FRE that is greatly in excess of previous assessments. New, paired samples of contemporaneous bone from terrestrial herbivores and omnivores (including humans) from Norse sites demonstrate at least some omnivore diets incorporated sufficient freshwater resources to result in a herbivore-omnivore age offset of up to 400 14C yrs. Modern samples of benthic detritus, aquatic plants, zooplankton, invertebrates and freshwater fish indicate an FRE in excess of 5000 14C yrs in some species. Likely geothermal mechanisms for this large FRE are discussed, along with implications for both chronological reconstruction and integrated investigation of stable and radioactive isotop
Direct Calculation of the Spin Stiffness in the -- Heisenberg Antiferromagnet
We calculate the spin stiffness for the frustrated
spin- Heisenberg antiferromagnet on a square lattice by exact
diagonalizations on finite clusters of up to sites followed by
extrapolations to the thermodynamic limit. For the non-frustrated case, we find
that , in excellent agreement with the best
results obtained by other means. Turning on frustration, the extrapolated
stiffness vanishes for . In this
intermediate region, the finite-size scaling works poorly -- an additional sign
that their is neither N\'eel nor collinear magnetic order. Using a hydrodynamic
relation, and previous results for the transverse susceptibility, we also
estimate the spin-wave velocity in the N\'eel-ordered region.Comment: 4 pages, uuencoded compressed ps-file (made with uufiles
Novel spin-liquid states in the frustrated Heisenberg antiferromagnet on the honeycomb lattice
Recent experiment on a honeycomb-lattice Heisenberg antiferromagnet (AF)
BiMnO(NO) revealed a novel spin-liquid-like behavior down to
low temperature, which was ascribed to the frustration effect due to the
competition between the AF nearest- and next-nearest-neighbor interactions
and . Motivated by the experiment, we study the ordering of the
- frustrated classical Heisenberg AF on a honeycomb lattice both by
a low-temperature expansion and a Monte Carlo simulation. The model has been
known to possess a massive degeneracy of the ground state, which, however,
might be lifted due to thermal fluctuations leading to a unique ordered state,
the effect known as 'order-by-disorder'. We find that the model exhibits an
intriguing ordering behavior, particularly near the AF phase boundary. The
energy scale of the order-by-disorder is suppressed there down to extremely low
temperatures, giving rise to exotic spin-liquid states like a "ring-liquid" or
a "pancake-liquid" state accompanied by the characteristic spin structure
factor and the field-induced antiferromagnetism. We argue that the recent
experimental data are explicable if the system is in such exotic spin-liquid
states
Topological quantum memory
We analyze surface codes, the topological quantum error-correcting codes
introduced by Kitaev. In these codes, qubits are arranged in a two-dimensional
array on a surface of nontrivial topology, and encoded quantum operations are
associated with nontrivial homology cycles of the surface. We formulate
protocols for error recovery, and study the efficacy of these protocols. An
order-disorder phase transition occurs in this system at a nonzero critical
value of the error rate; if the error rate is below the critical value (the
accuracy threshold), encoded information can be protected arbitrarily well in
the limit of a large code block. This phase transition can be accurately
modeled by a three-dimensional Z_2 lattice gauge theory with quenched disorder.
We estimate the accuracy threshold, assuming that all quantum gates are local,
that qubits can be measured rapidly, and that polynomial-size classical
computations can be executed instantaneously. We also devise a robust recovery
procedure that does not require measurement or fast classical processing;
however for this procedure the quantum gates are local only if the qubits are
arranged in four or more spatial dimensions. We discuss procedures for
encoding, measurement, and performing fault-tolerant universal quantum
computation with surface codes, and argue that these codes provide a promising
framework for quantum computing architectures.Comment: 39 pages, 21 figures, REVTe
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