485 research outputs found
Return times for Stochastic processes with power-law scaling
An analytical study of the return time distribution of extreme events for
stochastic processes with power-law correlation has been carried on. The
calculation is based on an epsilon-expansion in the correlation exponent:
C(t)=|t|^{-1+epsilon}. The fixed point of the theory is associated with
stretched exponential scaling of the distribution; analytical expressions,
valid in the pre-asymptotic regime, have been provided. Also the permanence
time distribution appears to be characterized by stretched exponential scaling.
The conditions for application of the theory to non-Gaussian processes have
been analyzed and the relations with the issue of return times in the case of
multifractal measures have been discussed.Comment: 9 pages, 5 figures, revtex
Der Bruch der Theorie in der Praxis durch Not
Some Remarks on Lujo Brentano's View of Labor Market Problems
Lujo Brentano (1844-1931) aimed for "realism" in economics. Regarding labor market theory, two topics are of particular interest: His investigations on "Hours and Wages in Relation to Production" (Scribner's 1894) and his analysis "On the History and Development of Gilds and the Origins of Trade Unions" (Trubner 1870). The topics of are discussed with a view on recent developments in labor economics.Lujo Brentano (1844-1931) hat sich als "realistischen" Ökonomen verstanden. Im Bereich der Arbeitsmarkttheorie sind zwei Bereiche von besonderem Interesse: Seine Untersuchungen über den Zusammenhang zwischen Lohn, Arbeitszeit und Arbeitsleistung und seine Überlegungen zur Bildung von kollektiven Formen der Lohnsetzung. Diese beiden Themen werden unter Einbeziehung gesamtwirtschaftlicher und methodischer Aspekte und einiger moderner Gesichtspunkte diskutiert
Radiative damping: a case study
We are interested in the motion of a classical charge coupled to the Maxwell
self-field and subject to a uniform external magnetic field, B. This is a
physically relevant, but difficult dynamical problem, to which contributions
range over more than one hundred years. Specifically, we will study the
Sommerfeld-Page approximation which assumes an extended charge distribution at
small velocities. The memory equation is then linear and many details become
available. We discuss how the friction equation arises in the limit of "small"
B and contrast this result with the standard Taylor expansion resulting in a
second order equation for the velocity of the charge.Comment: 4 figure
Effect of GnRH and its antagonist (Antarelix) on LH release from cultured bovine anterior pituitary cells
In the following investigations, the LH secretion of cells from pituitaries in heifers on days 16-18 of their oestrous cycle (n = 14) was analysed. Cells were dissociated with trypsin and collagenase and maintained in a static culture system. For the estimation of LH release, the cells were incubated with various concentrations of mammalian GnRH (Lutrelef) for 6h. To determine the action of Antarelix (GnRH antagonist), the cells were preincubated for 1 h with concentrations of 10-5 or 10-4 M Antarelix followed by 10-6 M GnRH coincubation for a further 6h. At the end of each incubation, the medium was collected for LH analysis. Parallel, intracellular LH was qualitatively detected by immunocytochemistry. Changes in the intensity of LH staining within the cells in dependence of different GnRH concentrations were not observed, but a significant increase LH secretion in pituitary cells was measured at 10-6 M GnRH. Antarelix had no effect on basal LH secretion at concentrations of 10-4 and 10-5 M. After coincubation of pituitary cells with Antarelix and GnRH, Antarelix blocked the GnRH-stimulated LH secretion with a maximal effect of 10-4 M, but the staining of immunoreactive intracellular LH was detected at approximately the same level compared to the pituitary cells treated with exogenous GnRH alone. These data demonstrate that Antarelix is effective in influencing the GnRH-stimulated LH secretion of pituitary cells in vitro. After administration of Antarelix in vivo, the GnRH-stimulated LH secretion of cultured pituitary cells was not inhibited
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Conformation and aggregation of selectively PEGylated and lipidated gastric peptide hormone human PYY3–36
The gastric peptide hormone human PYY3–36 is a target for the development of therapeutics, especially for treatment of obesity. The conformation and aggregation behavior of PEGylated and lipidated derivatives of this peptide are examined using a combination of fluorescence dye assays, circular dichroism (CD) spectroscopy, analytical ultracentrifugation (AUC) measurements, small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM). The behavior of two PYY3–36 derivatives lipidated (with octyl chains) in different positions is compared to that of two derivatives with PEG attached at different residues and to that of the native peptide. We find that, unexpectedly, PYY3–36 forms amyloid fibril structures above a critical aggregation concentration. Formation of these structures is suppressed by PEGylation or lipidation. PEGylation significantly reduces the (reversible) loss of α-helix content observed on heating PYY3–36. The PEG conjugates form mainly monomeric structures in solution- coiled-coil formation, and other aggregation presumably being sterically hindered by swollen PEG chains. However, some small aggregates are detected by AUC. In complete contrast, both of the two lipidated peptides show the formation of spherical micelle-like structures which are small oligomeric aggregates. Our findings show that PEGylation and lipidation are complementary strategies to tune the conformation and aggregation of the important gastric peptide hormone human PYY3–36
Synthesis of Substituted Bicyclo[2.2.2]octatrienes
An efficient route to bicyclo[2.2.2]octatriene, barrelene, and substituted versions of this molecule has been developed starting from the benzene equivalent cis-3,5-cyclohexadiene-1,2-diol. Following the Diels−Alder reaction of this molecule with an activated acetylene, conversion of the diol to the final olefin was accomplished through formation of a thiocarbonate intermediate and subsequent reaction with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine (DPD). The synthesis developed allows a variety of barrelenes to be prepared in as few as three steps from commercially available starting materials
Synthesis of Substituted Bicyclo[2.2.2]octatrienes
An efficient route to bicyclo[2.2.2]octatriene, barrelene, and substituted versions of this molecule has been developed starting from the benzene equivalent cis-3,5-cyclohexadiene-1,2-diol. Following the Diels−Alder reaction of this molecule with an activated acetylene, conversion of the diol to the final olefin was accomplished through formation of a thiocarbonate intermediate and subsequent reaction with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine (DPD). The synthesis developed allows a variety of barrelenes to be prepared in as few as three steps from commercially available starting materials
Enhanced stochastic oscillations in autocatalytic reactions
We study a simplified scheme of coupled autocatalytic reactions,
previously introduced by Togashi and Kaneko. The role of stochastic
fluctuations is elucidated through the use of the van Kampen system-size
expansion and the results compared with direct stochastic simulations. Regular
temporal oscillations are predicted to occur for the concentration of the
various chemical constituents, with an enhanced amplitude resulting from a
resonance which is induced by the intrinsic graininess of the system. The
associated power spectra are determined and have a different form depending on
the number of chemical constituents, . We make detailed comparisons in the
two cases and . Agreement between the theoretical and numerical
results for the power spectrum are good in both cases. The resulting spectrum
is especially interesting in the system, since it has two peaks, which
the system-size expansion is still able to reproduce accurately.Comment: Submitted to Phys. Rev.
Overtime working, the Phillips curve and the wage curve: British engineering, 1926-66
This paper shows that wage-unemployment elasticities derived from estimated wage curves and Phillips curves may be critically dependent on the measurement of wages. Incorporating hourly wage earnings, that include the influence of overtime payments, can lead to seriously distorted results. Meaningful elasticities are obtained only if hourly standard wages form the basis of analysis. Work is based on a unique data set describing two homogeneous blue-collar occupational groups - skilled fitters and unskilled labourers - in the British engineering industry. Each group is also divided into timeworkers and piece-rate workers. Data are aggregated into a panel of 28 local labour markets and cover the highly contrasting periods, 1928-1938 and 1954-1966
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