Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition

We investigate the dynamics of a large anisotropic spin whose easy-axis component is coupled to a bosonic bath with a spectral function J(\w)\propto \omega^s. Such a spin complex might be realized in a single-molecular magnet. Using the non-perturbative renormalization group, we calculate the line of quantum-phase transitions in the sub-ohmic regime ($s<1$). These quantum-phase transitions only occur for integer spin $J$. For half-integer $J$, the low temperature fixed-point is identical to the fixed-point of the spin-boson model without quantum-tunneling between the two levels. Short-time coherent oscillations in the spin decay prevail even into the localized phase in the sub-ohmic regime. The influence of the reorganization energy and the recurrence time on the decoherence in the absence of quantum-tunneling is discussed.Comment: 14 pages,7 figure

Carbon Isotope Constraints on the Deglacial CO2 Rise from Ice Cores

The stable carbon isotope ratio of atmospheric CO2 (d13Catm) is a key parameter in deciphering past carbon cycle changes. Here we present d13Catm data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in d13Catm during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the d13Catm evolution. During the Last Glacial Maximum, d13Catm and atmospheric CO2 concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then

Electron Paramagnetic Resonance Linewidths and Lineshapes for the Molecular Magnets Fe8 and Mn12

We study theoretically Electron Paramagentic Resonance (EPR) linewidths for single crystals of the molecular magnets Fe$_8$ and Mn$_{12}$ as functions of energy eigenstates $M_s$, frequency, and temperature when a magnetic field along the easy axis is swept at fixed excitation frequency. This work was motivated by recent EPR experiments. To calculate the linewidths, we use density-matrix equations, including dipolar interactions and distributions of the uniaxial anisotropy parameter $D$ and the Land\'{e} $g$ factor. Our calculated linewidths agree well with the experimental data. We also examine the lineshapes of the EPR spectra due to local rotations of the magnetic anisotropy axes caused by defects in samples. Our preliminary results predict that this effect leads to asymmetry in the EPR spectra.Comment: 2001 MMM conferenc

The role of the Tim8p–Tim13p complex in a conserved import pathway for mitochondrial polytopic inner membrane proteins

Tim23p is imported via the TIM (translocase of inner membrane)22 pathway for mitochondrial inner membrane proteins. In contrast to precursors with an NH2-terminal targeting presequence that are imported in a linear NH2-terminal manner, we show that Tim23p crosses the outer membrane as a loop before inserting into the inner membrane. The Tim8p–Tim13p complex facilitates translocation across the intermembrane space by binding to the membrane spanning domains as shown by Tim23p peptide scans with the purified Tim8p–Tim13p complex and crosslinking studies with Tim23p fusion constructs. The interaction between Tim23p and the Tim8p–Tim13p complex is not dependent on zinc, and the purified Tim8p–Tim13p complex does not coordinate zinc in the conserved twin CX3C motif. Instead, the cysteine residues seemingly form intramolecular disulfide linkages. Given that proteins of the mitochondrial carrier family also pass through the TOM (translocase of outer membrane) complex as a loop, our study suggests that this translocation mechanism may be conserved. Thus, polytopic inner membrane proteins, which lack an NH2-terminal targeting sequence, pass through the TOM complex as a loop followed by binding of the small Tim proteins to the hydrophobic membrane spanning domains

Thyroid hormones, blood plasma metabolites and haematological parameters in relationship to milk yield in dairy cows

To study their relationship to milk yield, the concentrations, in jugular venous blood, of thyroxine iodine (T4I), thyroxine (T4), 3,5,3'-tri-iodothyronine (T3), glucose, non-esterified fatty acids (NEFA), triglycerides, phospholipids, cholesterol, total protein, albumin, urea, haemoglobin and packed cell volume (PCV) have been measured in 36 cows (Simmental, Swiss Brown, Holstein and Simmental × Holstein) of different ages during a full lactation, pregnancy, dry period, parturition and 150 days of the ensuing lactation. Thyroid hormones and triglycerides were negatively, and total protein, globulin, cholesterol and phospholipids were positively, correlated with uncorrected or corrected milk yield during several periods of lactation, whereas glucose, NEFA, albumin, urea, haemoglobin and packed cell volume were not correlated with milk yield. The 10 animals with the highest milk yield (18·9 to 23·5 kg/day) exhibited significantly lower values of T4I, T4, T3 and glucose, significantly higher levels of total protein and globulin and tended to have higher levels of NEFA than the 10 cows with the lowest milk yield (10·9 to 14·3 kg/day) throughout or during certain periods of lactation, whereas concentrations of triglycerides, phospholipids, cholesterol, albumin, haemoglobin and PCV did not differ. Changes in T4I, T4, T3, glucose and total protein during lactation were also influenced by age, presumably associated with an increase in milk production with age. T3 was consistently lowest and cholesterol and phospholipids, during later stages of lactation, were highest in Holsteins, which had the highest milk yields of all breeds. Changes of blood parameters were mainly caused by shifts in energy and protein metabolism in association with level of milk productio

Measurements of CO2, its stable isotopes, O2/N2, and 222Rn at Bern, Switzerland

A one-year time series of atmospheric CO2 measurements from Bern, Switzerland, is presented. O2/N2 and Ar/N2 ratios as well as stable carbon and oxygen isotopes of CO2 and δ29N2, δ34O2 and δ36Ar were measured periodically during a one year period. Additionally, the 222Rn activity was measured during three months in the winter 2004. Using the correlation from short-term fluctuations of CO2 and 222Rn we estimated a mean CO2 flux density between February 2004 and April 2004 in the region of Bern of 95±39 tC km–2month–1. The continuous observations of carbon dioxide and associated tracers shed light on diurnal and seasonal patterns of the carbon cycle in an urban atmosphere. There is considerable variance in nighttime δ13C and δ18O of source CO2 throughout the year, however, with generally lower values in winter compared to summertime. The O2:CO2 oxidation ratio during the nighttime build-up of CO2 varies between –0.96 and –1.69 mol O2/mol CO2. Furthermore, Ar/N2 measurements showed that artifacts like thermal fractionation at the air intake are relevant for high precision measurements of atmospheric O2

Magnetic quantum coherence effect in Ni4 molecular transistors

We consider the electron transport in single molecule magnet transistors in the presence of Zeeman spin splitting and magnetic quantum coherence (MQC). The Zeeman interaction is extended along the leads, thereby producing gaps in the energy spectrum which allow electron transport with spin polarized along a certain direction. The MQC induces an effective coupling between localized spin states and continuum spin states in the single molecule magnet and leads, respectively. We investigate the conductance at zero temperature as a function of the applied bias and magnetic field, and show that the MQC is responsible for the appearence of resonances. Accordingly, we name them MQC resonances.Comment: 5 pages, Revtex

Analytical approach to semiconductor Bloch equations

Although semiconductor Bloch equations have been widely used for decades to address ultrafast optical phenomena in semiconductors, they have a few important drawbacks: (i) Coulomb terms between free electron-hole pairs require Hartree-Fock treatment which, in its usual form, preserves excitonic poles but loses biexcitonic resonances. (ii) Solving the resulting coupled differential equations imposes heavy numerics which completely hide the physics. This can be completely avoided if, instead of free electron-hole pairs, we use correlated pairs, i.e., excitons. Their interactions are easy to handle through the recently constructed composite-exciton many-body theory, which allows us to \emph{analytically} obtain the time evolution of the polarization induced by a laser pulse. This polarization comes from Coulomb interactions between virtual excitons, but also from Coulomb-free fermion exchanges, which are dominant at large detuning

Revision of an open-split-based dual-inlet system for elemental and isotope ratio mass spectrometers with a focus on clumped-isotope measurements

In this work, we present a revision of an open-split-based dual-inlet system for elemental and isotope ratio mass spectrometers (IRMSs), which was developed by the division of Climate and Environmental Physics of the University of Bern 2 decades ago. Besides discussing the corresponding improvements we show that with this inlet system (NIS-II, New Inlet System II) external precisions can be achieved that are high enough to perform measurements of multiply substituted isotopologues (clumped isotopes) on pure gases. For clumped-isotope ratios 35/32 and 36/32 of oxygen, we achieved standard deviations of 3.4×10-9 and 4.9×10-9, respectively, that we calculated from 60 interval means (20 s integration) of pure-oxygen gas measurements. Moreover, we report various performance tests and show that delta values of various air components can be measured with precisions of the order of tens of per meg and higher with the NIS-II. In addition, we demonstrate that our new open-split-based dual-inlet system allows us to measure some of these delta values with significantly higher precisions than an NIS-I (precursor of the NIS-II) and conventional changeover-valve-based dual-inlet systems (tests performed with two dual-inlet systems built by Elementar and Thermo Finnigan). Especially, our measurements point out that our inlet system provides reliable results at short idle times (20 s) and that the corresponding data do not need to be corrected for non-linearity. However, the sample consumption of our open-split-based dual-inlet system is several orders of magnitude higher than that of changeover-valve-based ones (0.33 sccm versus 0.005 sccm; standard cubic centimetres per minute). Due to the successful preliminary tests regarding measurements of clumped-isotope ratios, we will continue our work in this area to perform clumped-isotope studies according to common practices.</p