Mass gap effects and higher order electroweak Sudakov logarithms

The infrared structure of spontaneously broken gauge theories is phenomenologically very important and theoretically a challenging problem. Various attempts have been made to calculate the higher order behavior of large double-logarithmic (DL) corrections originating from the exchange of electroweak gauge bosons resulting in contradictory claims. We present results from two loop electroweak corrections for the process $g \longrightarrow f_{\rm R} {\bar f}_{\rm L}$ to DL accuracy. This process is ideally suited as a theoretical model reaction to study the effect of the mass gap of the neutral electroweak gauge bosons at the two loop level. Contrary to recent claims in the literature, we find that the calculation performed with the physical Standard Model fields is in perfect agreement with the results from the infrared evolution equation method. In particular, we can confirm the exponentiation of the electroweak Sudakov logarithms through two loops.Comment: 10 pages, 3 figures, LaTeX2e, uses epsfi

Flight Dynamics Operations of the TanDEM-X Formation

Since end of 2010 the German TerraSAR-X and TanDEM-X satellites are routinely operated as the first configurable single-pass Synthetic Aperture Radar interferometer in space. The two 1340 kg satellites fly in a 514 km sun-synchronous orbit. In order to collect sufficient measurements for the generation of a global digital elevation model and to demonstrate new interferometric SAR techniques and applications, more than three years of formation flying are foreseen with flexible baselines ranging from 150 m to few kilometers. As a prerequisite for the close formation flight an extensive flight dynamics system was established at DLR/GSOC, which comprises of GPS-based absolute and relative navigation and impulsive orbit and formation control. Daily formation maintenance maneuvers are performed by TanDEM-X to counterbalance natural and artificial disturbances. The paper elaborates on the routine flight dynamics operations and its interactions with mission planning and ground-station network. The navigation and formation control concepts and the achieved control accuracy are briefly outlined. Furthermore, the paper addresses non-routine operations experienced during formation acquisition, frequent formation reconfiguration, formation maintenance problems and space debris collision avoidance, which is even more challenging than for single-satellite operations. In particular two close approaches of debris are presented, which were experienced in March 2011 and April 2012. Finally, a formation break-up procedure is discussed which could be executed in case of severe onboard failures

An Analytical Expression for the Non-Singlet Structure Functions at Small xx in the Double Logarithmic Approximation

A simple analytic expression for the non-singlet structure function $f_{NS}$ is given. The expression is derived from the result of Ref. [1] obtained by low $x$ resummation of the quark ladder diagrams in the double logarithmic approximation of perturbative QCD.Comment: 5 pages, A few comments and refs are adde

First In-orbit Experience of TerraSAR-X Flight Dynamics Operations

TerraSAR-X is an advanced synthetic aperture radar satellite system for scientific and commercial applications that is realized in a public-private partnership between the German Aerospace Center (DLR) and the Astrium GmbH. TerraSAR-X was launched at June 15, 2007 on top of a Russian DNEPR-1 rocket into a 514 km sun-synchronous dusk-dawn orbit with an 11-day repeat cycle and will be operated for a period of at least 5 years during which it will provide high resolution SAR-data in the X-band. Due to the objectives of the interferometric campaigns the satellite has to comply to tight orbit control requirements, which are formulated in the form of a 250 m toroidal tube around a pre-flight determined reference trajectory. The acquisition of the reference orbit was one of the main and key activities during the Launch and Early Orbit Phase (LEOP) and had to compensate for both injection errors and spacecraft safe mode attitude control thruster activities. The paper summarizes the activities of GSOC flight dynamics team during both LEOP and early Commissioning Phase, where the main tasks have been 1) the first-acquisition support via angle-tracking and GPS-based orbit determination, 2) maneuver planning for target orbit acquisition and maintenance, and 3) precise orbit and attitude determination for SAR processing support. Furthermore, a presentation on the achieved results and encountered problems will be addressed

A General Lack of Compensation for Gene Dosage in Yeast

Gene copy number variation has been discovered in humans, between related species, and in different cancer tissues, but it is unclear how much of this genomic-level variation leads to changes in the level of protein abundance. To address this, we eliminated one of the two genomic copies of 730 different genes in Saccharomyces cerevisiae and asked how often a 50% reduction in gene dosage leads to a 50% reduction in protein level. For at least 80% of genes tested, and under several environmental conditions, it does: protein levels in the heterozygous strain are close to 50% of wild type. For < 5% of the genes tested, the protein levels in the heterozygote are maintained at nearly wild-type levels. These experiments show that protein levels are not, in general, directly monitored and adjusted to a desired level. Combined with fitness data, this implies that proteins are expressed at levels higher than necessary for survival

Thermal Spore Exposure Vessels

Thermal spore exposure vessels (TSEVs) are laboratory containers designed for use in measuring rates of death or survival of microbial spores at elevated temperatures. A major consideration in the design of a TSEV is minimizing thermal mass in order to minimize heating and cooling times. This is necessary in order to minimize the number of microbes killed before and after exposure at the test temperature, so that the results of the test accurately reflect the effect of the test temperature. A typical prototype TSEV (see figure) includes a flat-bottomed stainless-steel cylinder 4 in. (10.16 cm) long, 0.5 in. (1.27 cm) in diameter, having a wall thickness of 0.010 plus or minus 0.002 in. (0.254 plus or minus 0.051 mm). Microbial spores are deposited in the bottom of the cylinder, then the top of the cylinder is closed with a sterile rubber stopper. Hypodermic needles are used to puncture the rubber stopper to evacuate the inside of the cylinder or to purge the inside of the cylinder with a gas. In a typical application, the inside of the cylinder is purged with dry nitrogen prior to a test. During a test, the lower portion of the cylinder is immersed in a silicone-oil bath that has been preheated to and maintained at the test temperature. Test temperatures up to 220 C have been used. Because the spores are in direct contact with the thin cylinder wall, they quickly become heated to the test temperature

Running coupling constant and correlation length from Wilson loops

We consider a definition of the QCD running coupling constant $\alpha(\mu)$ related to Wilson loops of size $r{\times}t$ with arbitrary fixed $t/r$. The schemes defined by these couplings are very close to the $\overline{\rm MS}$ scheme (i.e.\ the one-loop perturbative correction to the coupling is small) for all values of $t/r$; in the $t/r\to\infty$ limit, the ``$q\bar q$ force'' scheme is recovered, where the coupling constant is related to the quark-antiquark force. We discuss the possibility of applying finite-size scaling techniques to the Monte Carlo evaluation of $\alpha(\mu)$ up to very large momentum scales. We propose a definition of correlation length, also related to Wilson loops, which should make such a computation feasible.Comment: 8 pages, latex (revtex