Chiral Corrections to Lattice Calculations of Charge Radii

Logarithmic divergences in pion and proton charge radii associated with chiral loops are investigated to assess systematic uncertainties in current lattice determinations of charge radii. The chiral corrections offer a possible solution to the long standing problem of why present lattice calculations yield proton and pion radii which are similar in size.Comment: PostScript file only. Ten pages. Figures included. U. of MD Preprint #92-19

The Rise of Certificate Transparency and Its Implications on the Internet Ecosystem

In this paper, we analyze the evolution of Certificate Transparency (CT) over time and explore the implications of exposing certificate DNS names from the perspective of security and privacy. We find that certificates in CT logs have seen exponential growth. Website support for CT has also constantly increased, with now 33% of established connections supporting CT. With the increasing deployment of CT, there are also concerns of information leakage due to all certificates being visible in CT logs. To understand this threat, we introduce a CT honeypot and show that data from CT logs is being used to identify targets for scanning campaigns only minutes after certificate issuance. We present and evaluate a methodology to learn and validate new subdomains from the vast number of domains extracted from CT logged certificates.Comment: To be published at ACM IMC 201

Diagnostik und Therapie der Harnleitersteinkolik

Summary: Acute ureteral colic presents with a complex of acute and characteristic flank pain that usually indicates the presence of a stone in the urinary tract. Diagnosis and management of renal colic have undergone considerable evolution and advancement in recent years. The application of noncontrast helical computed tomography (CT) in patients with suspected ureteral colic is one major advance in the primary diagnostic process. The superior sensitivity and specificity of helical CT allow ureterolithiasis to be diagnosed without the potential side effects of contrast media. Initial management is based on three key concepts: (A) rational and fast diagnostic process (B) effective pain control (C) and understanding of the impact of stone location and size on the natural course of the disease and definitive urologic management. These concepts are discussed in this review with reference to contemporary literatur

Sigma-term physics in the perturbative chiral quark model

We apply the perturbative chiral quark model (PCQM) at one loop to analyse meson-baryon sigma-terms. Analytic expressions for these quantities are obtained in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, axial nucleon coupling, strong pion-nucleon form factor) and of only one model parameter (radius of the nucleonic three-quark core). Our result for the piN sigma term of about 45 MeV is in good agreement with the value deduced by Gasser, Leutwyler and Sainio using dispersion-relation techniques and exploiting the chiral symmetry constraints.Comment: 19 pages, LaTeX-file, 2 Figure

Regularization, Renormalization and Range: The Nucleon-Nucleon Interaction from Effective Field Theory

Regularization and renormalization is discussed in the context of low-energy effective field theory treatments of two or more heavy particles (such as nucleons). It is desirable to regulate the contact interactions from the outset by treating them as having a finite range. The low energy physical observables should be insensitive to this range provided that the range is of a similar or greater scale than that of the interaction. Alternative schemes, such as dimensional regularization, lead to paradoxical conclusions such as the impossibility of repulsive interactions for truly low energy effective theories where all of the exchange particles are integrated out. This difficulty arises because a nonrelativistic field theory with repulsive contact interactions is trivial in the sense that the $S$ matrix is unity and the renormalized coupling constant zero. Possible consequences of low energy attraction are also discussed. It is argued that in the case of large or small scattering lengths, the region of validity of effective field theory expansion is much larger if the contact interactions are given a finite range from the beginning.Comment: 7 page

Nuclear matter in the chiral limit and the in-medium chiral condensate

We investigate nuclear matter, i.e. the nuclear equation-of-state (EOS) as well as the relativistic mean fields in the chiral limit. The investigations are based on a chiral nucleon-nucleon EFT interaction where the explicit and implicit pion mass dependence is known up to next-to-leading order. The nuclear bulk properties are found to remain fairly stable in the chiral limit. Based on the same interaction the in-medium scalar condensate is derived, both in Hartree-Fock approximation as well as from the Brueckner G-matrix, making thereby use of the Hellman-Feynman theorem. Short distance physics which determines the reduction of the in-medium nucleon mass is found to play only a minor role for the reduction of the chiral condensate.Comment: 30 pages, 5 figs. To appear in Nuclear Physics

Nucleon Magnetic Moments Beyond the Perturbative Chiral Regime

The quark mass dependence of nucleon magnetic moments is explored over a wide range. Quark masses currently accessible to lattice QCD, which lie beyond the regime of chiral perturbation theory (chiPT), are accessed via the cloudy bag model (CBM). The latter reproduces the leading nonanalytic behavior of chiPT, while modeling the internal structure of the hadron under investigation. We find that the predictions of the CBM are succinctly described by the simple formula, \mu_N(m_\pi) = \mu^{(0)}_N / (1 + \alpha m_\pi + \beta m_\pi^2), which reproduces the lattice data, as well as the leading nonanalytic behavior of chiPT. As this form also incorporates the anticipated Dirac moment behavior in the limit m_\pi \to \infty, it constitutes a powerful method for extrapolating lattice results to the physical mass regime.Comment: Revised version accepted for publication includes a new section demonstrating extrapolations of lattice QCD result

Variations of Hadron Masses and Matter Properties in Dense Nuclear Matter

Using a self-consistent quark model for nuclear matter we investigate variations of the masses of the non-strange vector mesons, the hyperons and the nucleon in dense nuclear matter (up to four times the normal nuclear density). We find that the changes in the hadron masses can be described in terms of the value of the scalar mean-field in matter. The model is then used to calculate the density dependence of the quark condensate in-medium, which turns out to be well approximated by a linear function of the nuclear density. Some relations among the hadron properties and the in-medium quark condensate are discussed.Comment: 22 pages, University of Adelaide preperint ADP-94-20/T160, submitted to Physical Review

A three dimensional finite element model for arterial clamping

Motivation and Introduction Arterial clamps are chosen to compress arteries during surgery so that blood flow is arrested. Arterial compression, however, may lead to injuries of the vessel wall, which are associated with a variety of severe short-term and long-term complications. For example, clamp induced injuries may cause spontaneous occlusion of the vessel after the operation, which leads to infarction of the downstream tissues. Therefore, surgeons require arterial clamps that allow efficient compression and cause only minimal injury. Severity and distribution of injuries depend on ͑i͒ the arterial type ͓1,2͔, the geometry and the nonlinear and anisotropic material behavior of the clamped multi-layered artery, ͑ii͒ the design of the chosen clamp ͓3-7͔ and ͑iii͒ the applied clamping forces ͓2,6,8,9͔. The optimization of this mechanical problem requires a numerical model, which considers appropriately all decisive factors. Yet, such a model is not available in the literature to date. Appropriate numerical models may lead to substantial improvements of arterial clamp designs, and thus are of potential interest for surgeons and clamp suppliers. In the past the demand for appropriate arterial clamps has led to a great variety of different designs and techniques. A suitable clamp design provides easy handling, good vessel grip and efficient vessel occlusion, and it is aimed to minimize arterial injuries. Clamps are named after their inventors as, for example, Blalock, Cooley, DeBakey, Fogarty, Potts, Satinsky, etc. They are available in different sizes with straight, curved or angled branches. Their jaws may be plain or have spikes, and they may be silicone filled. The existing designs are based on surgical intuition rather than on mechanical considerations. Consequently, the effects of clamping and the suitability of clamp designs have been investigated by means of experimental studies rather than by mechanical analyses. To the authors' knowledge, only ͓10͔ presented a mathematical approach with the goal to determine the minimum vascular occlusive force. However, this simplifying analytical model does not consider the crucial constitutive behavior of arterial walls. Thus, it is incapable of calculating wall stresses. Despite the clinical significance of arterial clamping there are relatively few studies, which are concerned with its local effects. Most of the experimental investigations are animal studies and focus on morphological changes. The observed injuries range from mild damage, which involves only the intima, to severe damage with total disruptions of the media, layer delaminations and even total wall disruptions with associated bleeding. In addition, long-term changes such as stenoses ͓11͔ and intimal hyperplasia-excessive thickening of the intima due to tissue growth ͓1͔-have been observed. Beside structural changes also functional changes of clamped arteries have been investigated, for example, the ability to relax or contract upon application of certain drugs ͓7,8͔ and the ability to inhibit blood clotting ͓12,13͔. The influences of the clamping force ͓2,6,8,9͔ and of the duration of clamping ͓14͔ have been studied. Moreover, comparisons of different types of arteries ͓2͔ and different clamp designs ͓3-7͔ in regard to clamp induced wall injury have been performed. These studies have identified the types and the consequences of clamp induced injuries and thus have demonstrated the importance of proper clamp designs. However, experimental studies are afflicted with a number of disadvantages. They are expensive and time-consuming and it is disputable if results of animal arteries are representative for human arteries. The significance of experimental studies is definitely restricted to the chosen arteries, instruments and clamping conditions. A fundamental shortcoming is that the results of existing experimental studies do not provide insights into the mechanical process of arterial clamping. The latter is determined by the three-dimensional stress-strain distributions in the clamped arterial wall. To overcome these shortcomings we developed a threedimensional finite element model for arterial clamping. The essential approach is to model the artery as a two-layer fiber-reinforced material with the fibers corresponding to the collagenous component of the material. The two layers represent the media ͑the middle layer of the artery͒ and the adventitia ͑the outer layer͒. Th