Bielefeld University

About: Bielefeld University is a education organization based out in Bielefeld, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Population & Quantum chromodynamics. The organization has 10123 authors who have published 26576 publications receiving 728250 citations. The organization is also known as: University of Bielefeld & UNIVERSITAET BIELEFELD.

Oxalic acid as a heterogeneous ice nucleus in the upper troposphere and its indirect aerosol effect

Abstract: . Heterogeneous ice freezing points of aqueous solutions containing various immersed solid dicarboxylic acids (oxalic, adipic, succinic, phthalic and fumaric) have been measured with a differential scanning calorimeter. The results show that only the dihydrate of oxalic acid (OAD) acts as a heterogeneous ice nucleus, with an increase in freezing temperature between 2 and 5 K depending on solution composition. In several field campaigns, oxalic acid enriched particles have been detected in the upper troposphere with single particle aerosol mass spectrometry. Simulations with a microphysical box model indicate that the presence of OAD may reduce the ice particle number density in cirrus clouds by up to ~50% when compared to exclusively homogeneous cirrus formation without OAD. Using the ECHAM4 climate model we estimate the global net radiative effect caused by this heterogeneous freezing to result in a cooling as high as −0.3 Wm−2.

Narrowband tunable VUV radiation generated by nonresonant sum- and difference-frequency mixing in xenon and krypton.

Abstract: Nonresonant sum- and difference-frequency mixing of the fundamental omega(L) and the second harmonic omega(UV) radiation of a powerful narrowband pulsed dye laser system excited by an Nd:YAG laser (lambda(L) = 5500-6500 A) generates intense VUV radiation in krypton and xenon with the frequency omega(VUV) = 2omega(UV) micro omega(L) The sum-frequency is tunable in spectral regions of negative dispersion between 1100 and 1300 A The maximum VUV pulse power exceeds 20 W (5 x 10(10) photons/pulse) VUV light pulses with up to 60 W (23 x 10(11) photons/pulse) are provided by the difference-frequency at wavelengths between 1850 and 2070 A In addition the conversion process omega(VUV) = 2omega(UV) - omega(IR) (omega(IR) is the frequency of the Nd:YAG laser) generates radiation in the wavelength range of 1595-1866 A With present laser systems the tuning range of the difference-frequency could be extended to wavelengths as short as 1226 A The sum- and difference-frequency conversion will thus provide intense coherent VUV light continuously tunable between 1100 and 2100 A

Single unit activity in the peripheral lateral line system of the cichlid fish Sarotherodon niloticus L.

Abstract: The activities of single afferent fibers were recorded in the trunk lateral line nerve of the cichlid fishSarotherodon niloticus L. Using both electrophysiological recordings and neuroanatomical tracing techniques, the number, arrangement, and innervation of superficial (SNs) and canal (CNs) neuromasts were determined. Both, SNs and CNs, are innervated by several afferent fibers of different diameters and efferent fibers. The CNs and SNs are neuronally separated: afferent fibers which innervate both CNs and SNs were not found. Whereas the single CN is innervated by a separate set of afferent fibers, fibers innervating the SNs within rows often branched to reach all or several SNs. The SNs within a row were thus considered to form a functional unit. With the exception of SNs on the tail fin, functional units of neuromasts were in general topographically restricted to single scales. The majority of lateral line units had resting activity. On the basis of the time interval distribution of the resting activity, 4 types of units were classified: these were labelled irregular (type I), regular (type II), bimodal (type III) and silent (type IV). Type I was the most common type of resting activity (obtained in 47.8% of the recorded units). Units with this resting activity type were identified as afferents innervating either SNs or CNs. Units with resting activity of type II represented mostly afferents of CNs if their mean activity was high (around 40 imp/s). If the mean activity of this type was below 20 imp/s the units were unresponsive to local water movements and at least some were identified as efferent fibers. Resting activity of type III was found only in units originating from CNs. Only 4% of the units were silent (type IV). These units were often identified as injured neuromasts. Units originating from CNs show higher mean resting activity than those from SNs. For both SN and CN units, the mean discharge rate of the resting activity correlated with the sensitivity to stimulation for sinusoidal water movements. During stimulation of the neuromasts by sinusoidal water movements of small amplitude and different frequencies, the response characteristics of SN and CN units were determined by linear frequency analysis under steady state conditions. Most units responded linearly to small stimulus amplitudes. In this amplitude range the units' resting activity was modulated according to the stimulus frequency. Small stimulus amplitudes proportionally changed the amount of modulation but did not alter the phase of the response. CN and SN units that responded linearly produce differing frequency responses. Whereas CNs were most sensitive at frequencies of up to 200 Hz (center frequencies between 100 and 200 Hz), the center frequencies of SNs were distributed between 10 and 70 Hz with a maximum number at about 30 Hz. Bode plots for many CN and SN units indicated that the neuromasts were sensitive to the acceleration component of the water movement. The functional significance of the differences between the two types of lateral line neuromasts (SNs and CNs) were discussed.

An all-sky search for continuous gravitational waves in the Parkes Pulsar Timing Array data set

Abstract: We present results of an all-sky search in the Parkes Pulsar Timing Array (PPTA) Data Release 1 data set for continuous gravitational waves (GWs) in the frequency range from 5 x 10(-9) to 2 x 10(-7) Hz. Such signals could be produced by individual supermassive binary black hole systems in the early stage of coalescence. We phase up the pulsar timing array data set to form, for each position on the sky, two data streams that correspond to the two GW polarizations and then carry out an optimal search for GW signals on these data streams. Since no statistically significant GWs were detected, we place upper limits on the intrinsic GW strain amplitude h(0) for a range of GW frequencies. For example, at 10(-8) Hz our analysis has excluded with 95 per cent confidence the presence of signals with h(0) >= 1.7 x 10(-14). Our new limits are about a factor of 4 more stringent than those of Yardley et al. based on an earlier PPTA data set and a factor of 2 better than those reported in the recent Arzoumanian et al. paper. We also present PPTA directional sensitivity curves and find that for the most sensitive region on the sky, the current data set is sensitive to GWs from circular supermassive binary black holes with chirp masses of 10(9) M-circle dot out to a luminosity distance of about 100 Mpc. Finally, we set an upper limit of 4 x 10(-3) Mpc(-3) Gyr(-1) at 95 per cent confidence on the coalescence rate of nearby (z less than or similar to 0.1) supermassive binary black holes in circular orbits with chirp masses of 10(10) M-circle dot.

The redox-sensitive transcription factor Rap2.4a controls nuclear expression of 2-Cys peroxiredoxin A and other chloroplast antioxidant enzymes

Abstract: The regulation of the chloroplast antioxidant capacity depends on nuclear gene expression. For the 2-Cys peroxiredoxin-A gene (2CPA) a cis-regulatory element was recently characterized, which responds to photosynthetic redox signals. In a yeast-one-hybrid screen for cis-regulatory binding proteins, the transcription factor Rap2.4a was isolated. Rap2.4a controls the transcript abundance of the prominent chloroplast antioxidant enzyme through binding to the CGCG core of a CE3-like element. Rap2.4a activity is regulated by dithiol/disulfide transition of regulatory cysteinyl residues and subsequent changes in the quaternary structure. The mid-point redox potential of Rap2.4a activation is -269 mV (pH 7.0). The redox sensitivity of Rap2.4a establishes an efficient switch mechanism for redox control of nuclear gene activity of chloroplast antioxidants, in which Rap2.4 is a redox-sensor and a transducer of redox information.