Showing papers by "Bielefeld University published in 1990"
TL;DR: In this paper, a method to calculate the elastic scattering amplitude at low energies in two-dimensional quantum field theories is proposed and tested in a numerical simulation of the O(3) non-linear σ-model on a simple square lattice.
651 citations
TL;DR: In this article, the authors introduce the quantized enveloping algebras (quantum groups) associated to a symmetric Kac-Moody Lie algebra via Hall algebra of Z/2-graded complexes of quiver representations.
Abstract: The Hall algebra of a finitary category encodes its extension structure. The story starts from the work of Steinitz on the module category of an abelian p-group, where the Hall algebra is the algebra of symmetric functions. The theory of Hall algebras is highlighted by Ringel around the 90’s in his seminal work realizing a half of a quantum group via the Hall algebra of quiver representations. Further developments include Lusztig’s canonical bases, cluster categories (Caldero-Keller), higher genus quantum algebras (Burban-Schiffmann, Schiffmann-Vasserot) – just to name a few. One of the goals of the seminar is to introduce Bridgeland’s construction of the quantized enveloping algebras (quantum groups) associated to a symmetric Kac-Moody Lie algebra via Hall algebras of Z/2-graded complexes of quiver representations and several recent progresses around it. In the last part of this seminar, we try to open the window to some applications of Hall algebras to mathematical physics via Hall algebra of curves: for example, they play an important rôle in the proof of AGT conjecture concerning pure N = 2 gauge theory for the group SU(r) ([SV]).
613 citations
TL;DR: A series of broad-host-range expression and lac fusion vectors, based on RSF1010 derivatives, was constructed, allowing the identification and characterization of promoter-carrying cloned fragments on the translational level, whereas the transcriptional fusion vectors can be used to identify and to study promoters on cloned fragment.
251 citations
TL;DR: In this article, structural equation models were used to investigate the validity of the 5-factor model of personality ratings. But, the results showed that the five factors that were obtained matched conventional measures of the Big Five very well.
248 citations
TL;DR: The aim of the current investigation was to look for measurable values corresponding to the hypothetical cost functions of the shoulder, elbow and wrist joints, and found that the cost functions seem to depend on joint angle and on the force which is necessary to hold the joint in a given position.
Abstract: The aim of our investigation is to understand the mechanisms which control the movement of the human arm. The arm is here considered as a redundant system: the shoulder, elbow and wrist joints, which provide three degrees of freedom, combine to move the hand in a horizontal plane, i.e. a two dimensional space. Thus the system has one extra degree of freedom. Earlier investigations of the static situation led to the hypothesis that independent cost functions were attached to each of the three joints and that the configuration chosen for a given target position is that which provides the minimum total cost (Cruse 1986). The aim of the current investigation was to look for measurable values corresponding to the hypothetical cost functions. Experiments using pointers of different lengths attached to the hand showed that the strategy in choosing the joint angles are independent of the limb length. The muscle force necessary to reach a given angle is increased by a spring mounted across a joint. In this situation the angles of the loaded joint are changed for a given target point to give way to the force effect. This leads to the conclusion that the hypothetical cost functions are not independent of the physiological costs necessary to hold the joint at a given angle. The cost functions seem to depend on joint angle and on the force which is necessary to hold the joint in a given position. Cost functions are measured by psychophysical methods. The results showU-shaped curves which can be approximated by parabolas. The position of minimum cost (maximum comfort) for one joint showed no or weak dependency on the angles of the other joints. For each subject these "psychophysical" cost functions are compared with the hypothetical cost functions. The comparison showed reasonable agreement. This supports the assumption that the psychophysically measured "comfort functions" provide a measure for the hypothetical cost functions postulated to explain the targeting movements. Targeting experiments using a four joint arm which has two extra degrees of freedom showed a much larger scatter compared to the three joint arm. Nevertheless, the results still conform to the hypothesis that also in this case the minimum cost principle is applied to solve the redundancy problem. As the cost function for the whole arm shows a large minimum valley, quite a large range of arm positions is possible of about equal total costs. The scatter does not result from pure randomness but seems to be mainly produced by the fact that the angles at the end of the movement depend on the value of the joint angles at the beginning of the movement.
204 citations
TL;DR: In this article, it was shown that the problem of finding an asymptotic formula for the number of integral points in a region on the ellipsoid q(x l..,... x r ) = n as n--+ oo where q is a positive definite integral quadratic form.
Abstract: It is a classical problem to find an asymptotic formula for the number of integral points in a region on the ellipsoid q(x l . . . . . x r ) = n as n--+ oo where q is a positive definite integral quadratic form. In particular, one wants to prove that the integral points on such an ellipsoid are asymptotically uniformly distributed. For r > 4, this problem has been solved by Pommerenke [Pom] (with some necessary restrictions on the set of numbers in which n tends to infinity if r = 4). Improvements of the error term have been obtained in [Ma, Pod, Go-Fo l ] . The case r = 3 has remained open so far; in fact one could not even give an unconditional proof of such a formula for the number of integral points on the whole ellipsoid (i.e., the number of representations of n by the quadratic form q). Linnik's ergodic method has been applied to this problem by several authors (see [Pe, Tel and references given there). However, the method requires imposing a condition on the quadratic residue character of n modulo some fixed prime. In order to remove it one has to assume certain unproved hypotheses concerning zeros of Dirichlet L-functions. Recent advances in the theory of modular forms of half integral weight [I, Du] as well as in the theory of quadratic forms [SP1, SP2, SP3] make it now possible to obtain the desired asymptotic formula unconditionally for r = 3 following the well known approach that has been succesful for r>4 . The only restrictions still present resemble those for r=4 . How this may be done for a 3-dimensional sphere has been shown in [Du] and [-Go-Fo2]. Although each single step of this proof is in the literature, it might be of some interest to collect them in one place and thus make this beautiful result more easily accessible. Since it does not involve much extra work, we also allow congruence conditions on the integral points.
191 citations
TL;DR: 'leakage' between perceptual/memory systems previously considered to be modality-specific is proposed as the mechanism for CMP, and the suggestion is made that one pathway for such leakage is through the ventral claustrum.
169 citations
TL;DR: Young zebra finch males were tested for their ability to acquire species-specific song before reaching independence and song copies developed by males kept with their fathers up to 35 days posthatching were as complete as those of males that remained in contact with their dads until day 100, when song crystallization has finished.
159 citations
TL;DR: In this article, a review of the gas-phase chemistry of protonated alkylbenzenes is presented, which includes gas phase reactions of their radical cations and their prominent fragment ions, such as C7H7+ and C7hs+'.
Abstract: Mass spectrometry and ion chemistry of alkylbenzenes, today, is much more than the gas-phase reactions of their radical cations and their prominent fragment ions, such as C7H7+ and C7Hs+'. Indeed, the gas-phase chemistry of gaseous ions originating mainly from the electron impact (EI) ionization of alkylbenzenes has been investigated extensively for more than 35 years and has revealed to us numerous amazing insights in elementary chemical processes. Many of these aspects, covered in Part I of this review (l), are under continuous investigation. Nevertheless, this has been only half of the story. Mass spectrometry of alkylbenzenes also comprises the gas-phase chemistry of protonated alkylbenzenes. Interest in protonated alkylbenzenes developed with the introduction of chemical ionization (CI) mass spectrometry (2-6). Munson and Field (7) were the first to apply this method to alkylbenzenes. However, the much closer relevance of evenelectron, protonated arene ions to electrophilic aromatic substitution (8,9) in solution and synthetic organic chemistry in general has made the gas-phase ion chemistry of protonated alkylbenzenes an independently important topic of mass spectrometric research. At the same time it was found that protonated alkylbenzenes can be generated in superacidic media (10) and studied by nuclear magnetic resonance spectrometry as well as by other spectroscopic techniques (11-17). Furthermore, computational approaches were widely applied to estimate the intrinsic properties of these ions (18). Later, besides simple protonation, ion-molecule reactions were used to generate transient or collisionally stabilized adduct ions from electrophiles and aromatic substrates. In additions to CI mass spectrometry, newer and complementary techniques were applied, among them, ion cyclotron resonance [ICR (19-21)] and high-pressure chemical ionization mass spectrometry [HPCI, (22)], triple-stage quadrupole mass spectrometry [TQMS (23)], and radiolytic and nuclear fission
154 citations
TL;DR: A positive correlation between the parasite's duration of stay near the carcass and her chances of parasitizing the other female's brood and a negative effect of parasitism on the caring female's own reproductive success were shown.
151 citations
TL;DR: Female burying beetles Necrophorus vespilloides Herbst (Coleoptera: Silphidae) were allowed to lay eggs on a carcass and their subsequent behavior towards larvae added to the carcass was observed, and most females killed and ate larvae that could not have hatched from their own eggs because they were added long before their own larvae hatched.
Abstract: Female burying beetles Necrophorus vespilloides Herbst (Coleoptera: Silphidae) were allowed to lay eggs on a carcass and their subsequent behavior towards larvae added to the carcass was observed. Females did not discriminate against unrelated larvae if these were added within an hour after the females' own first larva had hatched (at the “right” time). Changing the spatial surroundings of the carcass had no effect on the females' readiness to exhibit care behavior. Neither did the age of the larvae added or the condition of the carcass affect the onset of maternal care. However, the females' response to larvae encountered was strongly time-dependent: most females killed and ate larvae that could not have hatched from their own eggs because they were added long before their own larvae hatched. The proportion of females accepting larvae added “to early” increased as the time their own larvae hatched approached. Larvae added to the carcass 2 or 3 days after the test females' own first larva had hatched were always accepted by females that had already started to feed larvae, but were often killed by females that were not feeding larvae. In the latter group of females, the tendency to kill larvae added was most pronounced if the females had already started to produce a second clutch of eggs at the time larvae were added.
TL;DR: Luhmann as discussed by the authors argued for conceptual changes in the ways we describe modem society, and argued that risk is not simply the lack of safety, but rather the possible damage that may result from one's own decisions.
Abstract: Luhmann, N., 1990. Technology, environment and social risk: a systems perspective. Industrial Crisis Quarterly, 4: 223-231. The paper pleads for conceptual changes in the ways we describe modem society. We may use the same words, but should replace the antonyms or re define their contexts. Technology can be conceived of as being not primarily a proven relation of cause and effect, but rather as a simplification within a causal context, a simplification that has its own consequences. Risk is not simply the lack of safety, but rather the possible damage that may result from one's own decisions. The antonym of risk, then, would be danger as possible damage stemming from external sources. Steering (or public policy) can be conceived as generating differences in order to minimize other differences, rather than controlling the state of the system.
TL;DR: In this paper, a variant of the greedy algorithm for weight functions defined on the system of m-subsets of a given set E and characterize completely those classes of weight functions for which this algorithm works are studied.
TL;DR: In this article, the Grothendieck group K(R mod) of all finitely generated R-modules modulo split exact sequences is the free abelian group with basis indexed by @ +.
TL;DR: species mate recognition is influenced differentially by the independent divergence of cues used in different sensory modalities, as they do in experiments restricted to visual cues.
TL;DR: A comprehensive review of alkylbenzenes and related compounds can be found in this paper, with a focus on positively charged aromatic species such as positively charged benzene and alkene.
Abstract: From the vantage point of an organic chemist, many previously obscure fragmentation and isomerization processes of gaseous organic ions have become chemically reasonable reaction pathways. The term scrambling, used formerly as a synonym for mechanistic dilemmas concerning crazy atoms, has almost vanished from mass spectrometry literature in recent years, mostly because of the recognition of well-defined ionic intermediates and reaction mechanisms occurring before, during, or even after the actual cleavage of a molecular bond. The conceptual links between organic mass spectrometry and general organic chemistry have grown in many ways. In this respect, positively charged aromatic species have played a key role, owing to their inherent stability. The investigation of alkylbenzenes, in particular, has been a central focus of mass spectrometry since its application to the analysis of petroleum and gasoline in the mid-twentieth century, and has provided much insight into the intrinsic stability and reactivity of organic ions. Besides, and in connection with, the evergreens of organic mass spectrometry (e.g., the C7H7+/C7H8+' ion problem and the McLafferty rearrangement), new information has emerged during three decades of investigating the mass spectrometry of alkylbenzenes. This two-part review summarizes the mass spectrometry of alkylbenzenes and related compounds. Part one collects the gas-phase chemistry of ionized alkylbenzenes and part two describes that of protonated alkylbenzenes. This is in part due to the different relations to organic chemistry of the open-shell, radical ions (M+') on the one hand, and closed-shell ions such as [M+H]+, on the other. These two classes of ions also have different relevance to analytic applications of mass spectrometry. The radical ions of alkylbenzenes are discussed in Part I, owing to their historical priority and their broad occurrence in standard electron ionization (EI) mass spectrometry. Protonated benzene and alkylbenzenes (al
TL;DR: The present simulation using the back-propagation algorithm shows that a simple network of only nine units — 3 sensory input units, 3 motor output units, and 3 hidden units — suffices for representation of the stick insect's movement to a target.
Abstract: When the stick insect walks, the middle and rear legs step to positions immediately behind the tarsus of the adjacent rostral leg. Previous reports have described this movement to a target as a relationship between the tarsus positions of the two legs in a Cartesian coordinate system. However, leg proprioceptors measure the position of the target leg in terms of joint angles and leg muscles bring the tarsus of the moving leg to the proper end-point by establishing appropriate angles at the joints. Representation of this task in Cartesian coordinates requires non-linear coordinate transformations; realizing such a transformation in the nervous system appears to require many neurons. The present simulation using the back-propagation algorithm shows that a simple network of only nine units -- 3 sensory input units, 3 motor output units, and 3 hidden units -- suffices. The simulation also shows that an analytic coordinate transformation can be replaced by a direct association of joint configurations in the moving leg with those in the target leg.
TL;DR: In this paper, the performance of a pulsed arc cluster ion source (PACIS) is demonstrated for pure metal cluster ions and anions as well as mixed metal-rare gas clusters.
TL;DR: Female implanted with oestradiol preferred songs of males of their foster-father subspecies, irrespective of whether these males had been cross-fostered or raised normally, indicating that females use macrostructural song features for subspecies recognition and that their song preferences are learnt.
TL;DR: It is shown that if the matrices P 1,…, P n are paracontracting in the same smooth, strictly convex norm and if the sequence j i ∞ i = 1 has certain regularity properties, then the above iterates converge.
TL;DR: In this paper, the authors argue that explanations are to be sought within the context of bureaucracy rather than in that of industrialization, and that the academic training of state engineers set a powerful role model in Continental Europe but was absent in Anglo-America.
Abstract: Summary The rise to dominance of school culture in engineering education took place much later in England and the U.S.A. than in France or Germany. Why? This comparative essay argues that explanations are to be sought within the context of bureaucracy rather than in that of industrialization. The academic training of state engineers set a powerful role model in Continental Europe but was absent in Anglo-America. Consequently, the academic training of engineers for the private sector of the economy started earlier in Continental Europe, and the professional strategies of the engineers included emulating the public service. During the late nineteenth century a general belief in education as a key to international competition joined forces with a thorough transformation of the economy in providing new job markets for engineers graduating from colleges and universities.
TL;DR: In this article, the acceptance probability of the hybrid Monte Carlo method applied to lattice QCD with dynamical fermions is investigated in detail, and the dependence upon the step-size and the parameters β, m q and V is investigated.
TL;DR: Two models are discussed here which replace this algorithmic model by a network model which solves the static problem of targeting movements of a human arm when restricted to a horizontal plane.
Abstract: In an earlier investigation (Cruse and Bruwer 1987) an algorithmic model was proposed which describes targeting movements of a human arm when restricted to a horizontal plane. As three joints at shoulder, elbow and wrist are allowed to move, the system is redundant. Two models are discussed here which replace this algorithmic model by a network model. Both networks solve the static problem, i.e. they provide the joint angles which the arm has to adopt in order to reach a given point in the workspace. In the first model the position of this point is given in the form ofx --y coordinates, the second model obtains this information by means of a retina-like input layer. The second model is expanded by a simple procedure to describe movements from a start to an end point. The results qualitatively correspond to those obtained from human subjects. The advantages of the network models in comparison to the algorithmic model are discussed.
01 Sep 1990
TL;DR: The problem of critical slowing down in Monte Carlo simulations and some methods to alleviate or overcome it are reviewed: overrelaxation, multigrid and cluster algorithms.
Abstract: The problem of critical slowing down in Monte Carlo simulations and some methods to alleviate or overcome it are reviewed: overrelaxation, multigrid and cluster algorithms.
TL;DR: In this article, the order parameter, the susceptibility and the normalized fourth cumulant g r with high precision on N σ 3 × 4 lattices (N σ =8,12,18 and 26) were calculated for SU(2) gauge theory at finite temperature.
TL;DR: A 2.1 kb DNA fragment of the recombinant plasmid pCS2, isolated from an aminoethyl cysteine (AEC)-resistant and lysine-producing Corynebacterium glutamicum mutant strain, and which confers AEC resistance and l Lysine production on the wild-type G. glutamicUM ATCC 13032 was analysed.
Abstract: A 2.1 kb DNA fragment of the recombinant plasmid pCS2, isolated from an aminoethyl cysteine (AEC)-resistant and lysine-producing Corynebacterium glutamicum mutant strain, and which confers AEC resistance and lysine production on the wild-type G. glutamicum ATCC 13032 was analysed. DNA sequence analysis of this fragment revealed three large open reading frames (ORFs). The incomplete ORF1 does not contain the 5' end of the coding region. ORF2, which uses the same reading frame as ORF1, is identical to the 3' end of ORF1 and encodes a putative protein of 172 amino acids (aa) and of Mr 18,584. ORF3 encodes a putative protein of 344 aa and of Mr 36,275. The amino acid sequences deduced from ORF1 and ORF2 display strong homologies to those of the alpha- and beta-subunits of the Bacillus subtilis aspartokinase II. It is therefore proposed that the incomplete ORF1, termed lysC alpha, encodes part of the alpha-subunit of the C. glutamicum aspartokinase whereas the complete ORF2, termed lysC beta, encodes the beta-subunit of the same enzyme. ORF2 is responsible for AEC resistance and lysine production due to a feedback-resistant aspartokinase. The amino acid sequence deduced from ORF3, termed asd, is highly homologous to that of the Streptococcus mutans aspartate beta-semialdehyde dehydrogenase (ASD). Plasmids carrying the C. glutamicum asd gene complemented Escherichia coli asd mutants. Increase in ASD activity by a factor of 30-60 was measured for C. glutamicum cells harbouring high copy-number plasmids with the C. glutamicum asd gene.
TL;DR: In this article, the cross sections for K-shell ionization have been calculated for light particle (electron, positron) impact using a simple correction which takes into account the acceleration of an incident electron by the target nuclear field.
11 Jul 1990
TL;DR: In this paper, the authors give a simple algorithm for constructing sparse spanners for arbitrary weighted graphs and apply this algorithm to obtain specific results for planar graphs and Euclidean graphs.
Abstract: Given a graph G, a subgraph G′ is a t-spanner of G, if for every u, v ∈ V, the distance from u to v in G′ is at most t times longer than the distance in G In this paper we give a very simple algorithm for constructing sparse spanners for arbitrary weighted graphs We then apply this algorithm to obtain specific results for planar graphs and Euclidean graphs We discuss the optimality of our results and present several nearly matching lower bounds
TL;DR: Une correlation entre le nombre d'œufs pondus et le poids de the carcasse existe seulement pour les petites carcasses.
Abstract: Cette etude porte sur la regulation possible de la taille de la couvee par N. v. en fonction de la taille de la carcasse qu'elle a trouvee pour y pondre ses œufs. Une correlation entre le nombre d'œufs pondus et le poids de la carcasse existe seulement pour les petites carcasses
TL;DR: In this article, the phase structure of the chiral SU(2) L ⊗ SU( 2) R scalar-fermion model on the lattice with on-site Yukawa coupling y and Wilson-Yukawa coupling w for positive y and w.