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Search Results: 1 - 10 of 292121 matches for " T. P. Doerr "
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A simple electrostatic model applicable to biomolecular recognition
T. P. Doerr,Yi-Kuo Yu
Physics , 2009, DOI: 10.1103/PhysRevE.81.031925
Abstract: An exact, analytic solution for a simple electrostatic model applicable to biomolecular recognition is presented. In the model, a layer of high dielectric constant material (representative of the solvent, water) whose thickness may vary separates two regions of low dielectric constant material (representative of proteins, DNA, RNA, or similar materials), in each of which is embedded a point charge. For identical charges, the presence of the screening layer always lowers the energy compared to the case of point charges in an infinite medium of low dielectric constant. Somewhat surprisingly, the presence of a sufficiently thick screening layer also lowers the energy compared to the case of point charges in an infinite medium of high dielectric constant. For charges of opposite sign, the screening layer always lowers the energy compared to the case of point charges in an infinite medium of either high or low dielectric constant. The behavior of the energy leads to a substantially increased repulsive force between charges of the same sign. The repulsive force between charges of opposite signs is weaker than in an infinite medium of low dielectric constant material but stronger than in an infinite medium of high dielectric constant material. The presence of this behavior, which we name asymmetric screening, in the simple system presented here confirms the generality of the behavior that was established in a more complicated system of an arbitrary number of charged dielectric spheres in an infinite solvent.
The Use of Albuterol in Young Infants Hospitalized with Acute RSV Bronchiolitis
Michael T. Del Vecchio,Laura E. Doerr,John P. Gaughan
Interdisciplinary Perspectives on Infectious Diseases , 2012, DOI: 10.1155/2012/585901
Abstract: Objective. To evaluate the effects of albuterol use in young infants admitted with respiratory syncytial virus (RSV) bronchiolitis with regards to length of time on supplemental oxygen and length of stay (LOS). To consider the possibility that albuterol use may increase the need for supplemental oxygen and increase LOS. Design, Setting, and Participants. Full-term infants between the ages of 11 days and 90 days (=316) were included in this retrospective study. Infants included were hospitalized with a diagnosis of RSV bronchiolitis at a university-affiliated children’s hospital. Results. In 4 of 5 severity groups, patients who received albuterol required more time on supplemental oxygen and had longer LOS. The differences only reached statistical significance in one of the severity groups in regards to LOS. Conclusions. The use of albuterol does not appear to be useful in the treatment of young infants with RSV bronchiolitis and may actually be harmful, in regards to increased supplemental oxygen need.
A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph
H. -P. Doerr,T. Steinmetz,R. Holzwarth,T. Kentischer und W. Schmidt
Physics , 2012, DOI: 10.1007/s11207-012-9960-5
Abstract: A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut f\"ur Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut f\"ur Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.
Rigorous treatment of electrostatics for spatially varying dielectrics based on energy minimization
O. I. Obolensky,T. P. Doerr,R. Ray,Yi-Kuo Yu
Physics , 2008, DOI: 10.1103/PhysRevE.79.041907
Abstract: A novel energy minimization formulation of electrostatics that allows computation of the electrostatic energy and forces to any desired accuracy in a system with arbitrary dielectric properties is presented. An integral equation for the scalar charge density is derived from an energy functional of the polarization vector field. This energy functional represents the true energy of the system even in non-equilibrium states. Arbitrary accuracy is achieved by solving the integral equation for the charge density via a series expansion in terms of the equation's kernel, which depends only on the geometry of the dielectrics. The streamlined formalism operates with volume charge distributions only, not resorting to introducing surface charges by hand. Therefore, it can be applied to any spatial variation of the dielectric susceptibility, which is of particular importance in applications to biomolecular systems. The simplicity of application of the formalism to real problems is shown with analytical and numerical examples.
Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel
R A Probst,L Wang,H-P Doerr,T Steinmetz,T J Kentischer,G Zhao,T W H?nsch,Th Udem,R Holzwarth,W Schmidt
Physics , 2015, DOI: 10.1088/1367-2630/17/2/023048
Abstract: We investigate a new scheme for astronomical spectrograph calibration using the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our concept is based upon a single-mode fiber channel, that simultaneously feeds the spectrograph with comb light and sunlight. This yields nearly perfect spatial mode matching between the two sources. In combination with the absolute calibration provided by the frequency comb, this method enables extremely robust and accurate spectroscopic measurements. The performance of this scheme is compared to a sequence of alternating comb and sunlight, and to absorption lines from Earth's atmosphere. We also show how the method can be used for radial-velocity detection by measuring the well-explored 5-minute oscillations averaged over the full solar disk. Our method is currently restricted to solar spectroscopy, but with further evolving fiber-injection techniques it could become an option even for faint astronomical targets.
Magnetic field induced Ising axis conversion in Tb0.5Dy0.5Cu2 single crystals
Loewenhaupt M.,Doerr M.,Rotter M.,Reif T.
Brazilian Journal of Physics , 2000,
Abstract: We study the Ising axis conversion in a mixed Tb0.5Dy0.5Cu2 single crystal. Interest is focused on how changes in the exchange interactions due to rare earth substitutions influence the existence of magnetic phases and the critical field values for the Ising axis conversion. From magnetisation measurements we determined the (H - T ) phase diagram for magnetic fields parallel to the easy a-axis and the temperature dependence of the critical field for the Ising axis conversion. Both properties for the mixed crystal follow a simple composition scaling behavior. But in contrast to previous studies on the pure compounds TbCu2 and DyCu2 the changes of magnetic and structural properties at the conversion cannot be recovered completely by thermal treatment. Only a small part (10 % of the sample volume) goes back to the virgin state after warming the sample to 500 K. This behavior is of great interest for further neutron or X-ray diffraction studies of the Ising axis conversion allowing to study the converted phase under routinely used experimental conditions.
Collecting Coupons with Random Initial Stake
Benjamin Doerr,Carola Doerr
Computer Science , 2013,
Abstract: Motivated by a problem in the theory of randomized search heuristics, we give a very precise analysis for the coupon collector problem where the collector starts with a random set of coupons (chosen uniformly from all sets). We show that the expected number of rounds until we have a coupon of each type is $nH_{n/2} - 1/2 \pm o(1)$, where $H_{n/2}$ denotes the $(n/2)$th harmonic number when $n$ is even, and $H_{n/2}:= (1/2) H_{\lfloor n/2 \rfloor} + (1/2) H_{\lceil n/2 \rceil}$ when $n$ is odd. Consequently, the coupon collector with random initial stake is by half a round faster than the one starting with exactly $n/2$ coupons (apart from additive $o(1)$ terms). This result implies that classic simple heuristic called \emph{randomized local search} needs an expected number of $nH_{n/2} - 1/2 \pm o(1)$ iterations to find the optimum of any monotonic function defined on bit-strings of length $n$.
Optimal Parameter Choices Through Self-Adjustment: Applying the 1/5-th Rule in Discrete Settings
Benjamin Doerr,Carola Doerr
Computer Science , 2015,
Abstract: While evolutionary algorithms are known to be very successful for a broad range of applications, the algorithm designer is often left with many algorithmic choices, for example, the size of the population, the mutation rates, and the crossover rates of the algorithm. These parameters are known to have a crucial influence on the optimization time, and thus need to be chosen carefully, a task that often requires substantial efforts. Moreover, the optimal parameters can change during the optimization process. It is therefore of great interest to design mechanisms that dynamically choose best-possible parameters. An example for such an update mechanism is the one-fifth success rule for step-size adaption in evolutionary strategies. While in continuous domains this principle is well understood also from a mathematical point of view, no comparable theory is available for problems in discrete domains. In this work we show that the one-fifth success rule can be effective also in discrete settings. We regard the $(1+(\lambda,\lambda))$~GA proposed in [Doerr/Doerr/Ebel: From black-box complexity to designing new genetic algorithms, TCS 2015]. We prove that if its population size is chosen according to the one-fifth success rule then the expected optimization time on \textsc{OneMax} is linear. This is better than what \emph{any} static population size $\lambda$ can achieve and is asymptotically optimal also among all adaptive parameter choices.
A Tight Runtime Analysis of the $(1+(λ, λ))$ Genetic Algorithm on OneMax
Benjamin Doerr,Carola Doerr
Computer Science , 2015,
Abstract: Understanding how crossover works is still one of the big challenges in evolutionary computation research, and making our understanding precise and proven by mathematical means might be an even bigger one. As one of few examples where crossover provably is useful, the $(1+(\lambda, \lambda))$ Genetic Algorithm (GA) was proposed recently in [Doerr, Doerr, Ebel: TCS 2015]. Using the fitness level method, the expected optimization time on general OneMax functions was analyzed and a $O(\max\{n\log(n)/\lambda, \lambda n\})$ bound was proven for any offspring population size $\lambda \in [1..n]$. We improve this work in several ways, leading to sharper bounds and a better understanding of how the use of crossover speeds up the runtime in this algorithm. We first improve the upper bound on the runtime to $O(\max\{n\log(n)/\lambda, n\lambda \log\log(\lambda)/\log(\lambda)\})$. This improvement is made possible from observing that in the parallel generation of $\lambda$ offspring via crossover (but not mutation), the best of these often is better than the expected value, and hence several fitness levels can be gained in one iteration. We then present the first lower bound for this problem. It matches our upper bound for all values of $\lambda$. This allows to determine the asymptotically optimal value for the population size. It is $\lambda = \Theta(\sqrt{\log(n)\log\log(n)/\log\log\log(n)})$, which gives an optimization time of $\Theta(n \sqrt{\log(n)\log\log\log(n)/\log\log(n)})$. Hence the improved runtime analysis gives a better runtime guarantee along with a better suggestion for the parameter $\lambda$. We finally give a tail bound for the upper tail of the runtime distribution, which shows that the actual runtime exceeds our runtime guarantee by a factor of $(1+\delta)$ with probability $O((n/\lambda^2)^{-\delta})$ only.
The Wave-Front Correction System for the Sunrise Balloon-Borne Solar Observatory
T. Berkefeld,W. Schmidt,D. Soltau,A. Bell,H. P. Doerr,B. Feger,R. Friedlein,K. Gerber,F. Heidecke,T. Kentischer,O. v. d. Lühe,M. Sigwarth,E. W?lde,P. Barthol,W. Deutsch,A. Gandorfer,D. Germerott,B. Grauf,R. Meller,A. Alvarez-Herrero,M. Kn?lker,V. Martinez Pillet,S. K. Solanki,A. M. Title
Physics , 2010, DOI: 10.1007/s11207-010-9676-3
Abstract: This paper describes the wave-front correction system developed for the Sunrise balloon telescope, and provides information about its in-flight performance. For the correction of low-order aberrations, a Correlating Wave-Front Sensor (CWS) was used. It consisted of a six-element Shack-Hartmann wave-front sensor (WFS), a fast tip-tilt mirror for the compensation of image motion, and an active telescope secondary mirror for focus correction. The CWS delivered a stabilized image with a precision of 0.04 arcsec (rms), whenever the coarse pointing was better than 90 arcsec peak-to-peak. The automatic focus adjustment maintained a focus stability of 0.01 waves in the focal plane of the CWS. During the 5.5 day flight, good image quality and stability was achieved during 33 hours, containing 45 sequences that lasted between 10 and 45 minutes.
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