Visuomotor delays when hitting running spiders.

In general, information about the environment (for instance a target) is not instantaneously available for the nervous system. A minimal delay for visual information to affect the movement of the hand is about 110 ms. However, if the movement of a target is predictable, humans can pursue it with zero delay. To make this prediction, information about the speed of the target is necessary. Our results show that this information is used with a delay of about 200 ms. We discuss that oculomotor efference is a likely source of information for this prediction

Self Trapping of a Single Bacterium in its Own Chemoattractant

Bacteria (e.g. E. Coli) are very sensitive to certain chemoattractants (e.g. asparate) which they themselves produce. This leads to chemical instabilities in a uniform population. We discuss here the different case of a single bacterium, following the general scheme of Brenner, Levitov and Budrene. We show that in one and two dimensions (in a capillary or in a thin film) the bacterium can become self-trapped in its cloud of attractant. This should occur if a certain coupling constant $g$ is larger than unity. We then estimate the reduced diffusion D_eff of the bacterium in the strong coupling limit, and find D_eff ~ 1/g.Comment: 4 pages, absolutely no figure

Quaternionic differential operators

Motivated by a quaternionic formulation of quantum mechanics, we discuss quaternionic and complex linear differential equations. We touch only a few aspects of the mathematical theory, namely the resolution of the second order differential equations with constant coefficients. We overcome the problems coming out from the loss of the fundamental theorem of the algebra for quaternions and propose a practical method to solve quaternionic and complex linear second order differential equations with constant coefficients. The resolution of the complex linear Schrodinger equation, in presence of quaternionic potentials, represents an interesting application of the mathematical material discussed in this paper.Comment: 25 pages, AMS-Te

Solving simple quaternionic differential equations

The renewed interest in investigating quaternionic quantum mechanics, in particular tunneling effects, and the recent results on quaternionic differential operators motivate the study of resolution methods for quaternionic differential equations. In this paper, by using the real matrix representation of left/right acting quaternionic operators, we prove existence and uniqueness for quaternionic initial value problems, discuss the reduction of order for quaternionic homogeneous differential equations and extend to the non-commutative case the method of variation of parameters. We also show that the standard Wronskian cannot uniquely be extended to the quaternionic case. Nevertheless, the absolute value of the complex Wronskian admits a non-commutative extension for quaternionic functions of one real variable. Linear dependence and independence of solutions of homogeneous (right) H-linear differential equations is then related to this new functional. Our discussion is, for simplicity, presented for quaternionic second order differential equations. This involves no loss of generality. Definitions and results can be readily extended to the n-order case.Comment: 9 pages, AMS-Te

From secondary to primary prevention of progressive renal disease: The case for screening for albuminuria

From secondary to primary prevention of progressive renal disease: The case for screening for albuminuria. Many subjects nowadays present with end-stage renal failure and its attendant cardiovascular complications without known prior renal damage. In this report we review the evidence available to strongly suggest that the present practice of secondary prevention in those with known prior renal disease should be extended to primary prevention for those subjects in the general population who are at risk for progressive renal failure, but who had never suffered from a primary renal disease. We show that such subjects can be detected by screening for albuminuria. Elevated urinary albumin loss is an indicator not only of poor renal, but also of poor cardiovascular prognosis. In addition to diabetic subjects who are at risk for albuminuria, we also show that hypertensive, obese, and smoking subjects are more susceptible. We suggest that therapies that have been shown to lower albumin excretion, such as ACE inhibitors, angiotensin II receptor antagonists, and statins be started early in such patients to prevent them from developing clinical renal disease and its attendant cardiovascular complications

Electrorotation of colloidal suspensions

When a strong electric field is applied to a colloidal suspension, it may cause an aggregation of the suspended particles in response to the field. In the case of a rotating field, the electrorotation (ER) spectrum can be modified further due to the local field effects arising from the many-particle system. To capture the local field effect, we invoke the Maxwell-Garnett approximation for the dielectric response. The hydrodynamic interactions between the suspended particles can also modify the spin friction, which is a key to determine the angular velocity of ER. By invoking the spectral representation approach, we derive the analytic expressions for the characteristic frequency at which the maximum angular velocity of ER occurs. From the numerical caculation, we find that there exist two sub-dispersions in the ER spectrum. However, the two characteristic frequencies are so close that the two peaks actually overlap and become a single broad peak. We report a detailed investigation of the dependence of the characteristic frequency and the dispersion strength of ER on various material parameters.Comment: RevTeX, 4 eps figures; clarifying discussion added in accord with referees' reports; accepted by Physics Letters

Max Clara and Innsbruck - The origin of a German Nationalist and National Socialist career.

This investigation aims to summarize hitherto scattered pieces of evidence of the early biography of Max Clara, especially considering his connections with the Histological Institute of the University of Innsbruck. Max Clara was born in 1899 in South Tyrol, at that time part of the Habsburg Empire. After high school in Bozen and his participation in World War I, Clara studied medicine in Innsbruck, Austria and Leipzig, Germany, graduating from Innsbruck University in 1923. He joined the Corps Gothia, a German Student Corps, at the start of his studies and became socialized as a German nationalist. When the Tyrolean Parliament conducted an illegal referendum in 1921, in which a majority voted for the merger of Tyrol with Germany, the active members of the Gothia spontaneously removed the border barriers between Austria and Bavaria in the municipality of Scharnitz. They brought them to Innsbruck to be deposited in the statehouse. Clara's participation in this activity is not documented but is very likely. Seventy-four per cent of the members of this corps joined the Nazi party (Nationalsozialistische Deutsche Arbeiterpartei, NSDAP), even before the annexation of Austria by National Socialist (NS) Germany in 1938. Clara likely met Maximinian de Crinis, an SS officer and high-ranking member of the NS health administration, through contacts within their respective corps. De Crinis supported Clara decisively in the anatomist's appointments as chair of anatomy at the University of Leipzig and later at the University of Munich. Initially, Clara began his academic career at the Institute of Histology and Embryology in Innsbruck as (student) demonstrator, and in 1923 as an assistant. In December 1923 Clara had to leave Innsbruck for Blumau, South Tyrol to take over the medical surgery of his father, who had passed away unexpectedly. Back in Italy, he continued his histological research in his spare time and published a large number of scientific papers. His connections with Innsbruck and especially with histologist Jurg Mathis never ceased

p53 mediates failure of human definitive hematopoiesis in dyskeratosis congenita

Summary: Dyskeratosis congenita (DC) is a bone marrow failure syndrome associated with telomere dysfunction. The progression and molecular determinants of hematopoietic failure in DC remain poorly understood. Here, we use the directed differentiation of human embryonic stem cells harboring clinically relevant mutations in telomerase to understand the consequences of DC-associated mutations on the primitive and definitive hematopoietic programs. Interestingly, telomere shortening does not broadly impair hematopoiesis, as primitive hematopoiesis is not impaired in DC cells. In contrast, while phenotypic definitive hemogenic endothelium is specified, the endothelial-to-hematopoietic transition is impaired in cells with shortened telomeres. This failure is caused by DNA damage accrual and is mediated by p53 stabilization. These observations indicate that detrimental effects of telomere shortening in the hematopoietic system are specific to the definitive hematopoietic lineages. This work illustrates how telomere dysfunction impairs hematopoietic development and creates a robust platform for therapeutic discovery for treatment of DC patients. : By directly assessing primitive or definitive hematopoiesis derived from telomerase-mutant hESCs, Batista and colleagues show that telomere shortening specifically impairs definitive hematopoietic potential, while primitive hematopoiesis is instead enhanced. This system offers the unprecedented capability to study hematopoietic failure and suggests that bone marrow failure in DC patients is reversible. Keywords: embryonic stem cells, hematopoiesis, bone marrow failure, telomerase, dyskeratosis congenita, disease modeling, telomeres, telomere damag