Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles

The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is, however, challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong interannual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (≳ 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new data with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely or small in magnitude (≪ 1 ‰ RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow

A study of the Jovian [S II] nebula at high spectral resolution

Observations of forbidden line S II λλ6716-6731 A emissions from the Jovian magnetosphere have been carried out with a PEPSIOS spectrometer at the Hale 5 m telescope. Spectral resolving power was sufficient to resolve the forbidden line S II line widths. From measured λλ6716-6731 A doublet ratios and spectral line widths a thermal plasma is found characterized by temperatures about 2 x 10^4 K and electron densities about ~2 x 10^3 cm^(-3). The source of forbidden line S II emissions was centered within a toroidal region of radius 5 Jupiter radii (inside the orbit of Io), with tight latitudinal confinement near the equilibrium equator for ions in the tilted corotating Jovian magnetic field, and significant long-lived longitudinal structure

Human pharmacokinetics and CSF penetration of clavulanic acid

Clavulanic acid, a product of Streptomyces clavuligerus with β-lactam structure, is a potent inhibitor of several β-lactamases. To study its pharmacokinetic and CSF penetration in patients without meningeal inflammation, a single oral dose of 250 mg of clavulanic acid was given to 21 patients. One patient was studied in a multiple dose schedule. Fifteen of these 21 patients had a diagnostic lumbar puncture and 3 neurosurgical patients had a continuous CSF drainage. Serum and urine concentrations of clavulanic acid were available from 22 patients. The mean peak serum concentration was 4·3 mg/l and individual peak serum concentrations ranged from 0·1-9·5 mg/i between 40 and 60 mm after ingestion of clavulanic acid. Urinary recovery between 300 and 400 mm ranged from 0·8-54·3% of the administered dose. The mean absorption half life was 0·26 h and the mean elimination half life was 0·9 h. Considerable degradation of clavulanic acid occurred in vitro at 37°C. In pooled human serum, phosphate buffer pH 7 and 5, an hourly loss of activity of about 10, 7 and 10% respectively, was observe

Leistungs- und Kostenrechnung in der Datenverarbeitung:Am Beispiel der Hochschulrechenzentren in NRW

Für Hochschulrechenzentren wird eine Leistungs- und Kostenrechnung vorgeschlagen, die Dienstleistungen und ihre Qualitätsmerkmale neben eine Prozeßkostenrechnung stellt. Mit der Prozeßkostenrechnung entstehen Steuerungs- und Vergleichsmöglichkeiten in und zwischen Hochschulrechenzentren. Über "Kostentreiber" werden die Leistungen weitgehend mengenabhängig. Eine Zuordnung der Kosten zu ihren Verursachern wird möglich. Die Prozesse werden für ein Hochschulrechenzentrum definiert, die einzelnen Kostenfaktoren erläutert und zusammengestellt. Es wird ein Berechnungsschema vorgeschlagen, Ausführungshinweise werden gegeben und die Ergebnisse diskutiert. Als Fallstudien werden die Prozeßkosten eines kleinen und eines großen Rechenzentrums angesprochen

Quantitative estimates of discrete harmonic measures

A theorem of Bourgain states that the harmonic measure for a domain in $\R^d$ is supported on a set of Hausdorff dimension strictly less than $d$ \cite{Bourgain}. We apply Bourgain's method to the discrete case, i.e., to the distribution of the first entrance point of a random walk into a subset of $\Z ^d$, $d\geq 2$. By refining the argument, we prove that for all \b>0 there exists \rho (d,\b)N(d,\b), any $x \in \Z^d$, and any $A\subset \{1,..., n\}^d$ | \{y\in\Z^d\colon \nu_{A,x}(y) \geq n^{-\b} \}| \leq n^{\rho(d,\b)}, where $\nu_{A,x} (y)$ denotes the probability that $y$ is the first entrance point of the simple random walk starting at $x$ into $A$. Furthermore, $\rho$ must converge to $d$ as \b \to \infty.Comment: 16 pages, 2 figures. Part (B) of the theorem is ne

Nonlinear photoluminescence spectra from a quantum dot-cavity system: Direct evidence of pump-induced stimulated emission and anharmonic cavity-QED

We investigate the power-dependent photoluminescence spectra from a strongly coupled quantum dot-cavity system using a quantum master equation technique that accounts for incoherent pumping, pure dephasing, and fermion or boson statistics. Analytical spectra at the one-photon correlation level and the numerically exact multi-photon spectra for fermions are presented. We compare to recent experiments on a quantum dot-micropiller cavity system and show that an excellent fit to the data can be obtained by varying only the incoherent pump rates in direct correspondence with the experiments. Our theory and experiments together show a clear and systematic way of studying stimulated-emission induced broadening and anharmonic cavity-QED.Comment: We have reworked our previous arXiv paper and submitted this latest version for peer revie

Hypersurface Bohm-Dirac models

We define a class of Lorentz invariant Bohmian quantum models for N entangled but noninteracting Dirac particles. Lorentz invariance is achieved for these models through the incorporation of an additional dynamical space-time structure provided by a foliation of space-time. These models can be regarded as the extension of Bohm's model for N Dirac particles, corresponding to the foliation into the equal-time hyperplanes for a distinguished Lorentz frame, to more general foliations. As with Bohm's model, there exists for these models an equivariant measure on the leaves of the foliation. This makes possible a simple statistical analysis of position correlations analogous to the equilibrium analysis for (the nonrelativistic) Bohmian mechanics.Comment: 17 pages, 3 figures, RevTex. Completely revised versio