A study of the entanglement in systems with periodic boundary conditions

We define the local periodic linking number, LK, between two oriented closed or open chains in a system with three-dimensional periodic boundary conditions. The properties of LK indicate that it is an appropriate measure of entanglement between a collection of chains in a periodic system. Using this measure of linking to assess the extent of entanglement in a polymer melt we study the effect of CReTA algorithm on the entanglement of polyethylene chains. Our numerical results show that the statistics of the local periodic linking number observed for polymer melts before and after the application of CReTA are the same.Comment: 11 pages, 11 figure

Computer-assisted ex vivo, normothermic small bowel perfusion

Background: In the present study, a technique for computer-assisted, normothermic, oxygenated, ex vivo, recirculating small bowel perfusion was established as a tool to investigate organ pretreatment protocols and ischemia/reperfusion phenomena. A prerequisite for the desired setup was an organ chamber for ex vivo perfusion and the use of syngeneic whole blood as perfusate. Methods: The entire small bowel was harvested from Lewis rats and perfused in an organ chamber ex vivo for at least 2 h. The temperature was kept at 37 degrees C in a water bath. Three experimental groups were explored, characterized by different perfusion solutions. The basic perfusate consisted of syngeneic whole blood diluted with either NaCl, Krebs' solution or Krebs' solution and norepinephrine to a hematocrit of 30%. In addition, in each group l-glutamine was administered intraluminally. The desired perfusion pressure was 100 mm Hg which was kept constant with a computer-assisted data acquisition software, which measured an-line pressure, oxygenation, flow, temperature and pH and adjusted the pressure by changing the flow via a peristaltic pump. The viability of the preparation was tested by measuring oxygen consumption and maltose absorption, which requires intact enzymes of the mucosal brush border to break down maltose into glucose. Results: Organ perfusion in group 1 (dilution with NaCl) revealed problems such as hypersecretion into the bowel lumen, low vascular resistance and no maltose uptake. In contrast a viable organ could be demonstrated using Krebs' solution as dilution solution. The addition of norepinephrine led to an improved perfusion over the entire perfusion period. Maltose absorption was comparable to tests conducted with native small bower. Oxygen consumption was stable during the 2-hour perfusion period. Conclusions: The ex vivo perfusion system established enables small bowel perfusion for at least 2 h. The viability of the graft could be demonstrated. The perfusion time achieved is sufficient to study leukocyte/lymphocyte interaction with the endothelium of the graft vessels. In addition, a viable small bowel, after 2 h of ex vivo perfusion, facilitates testing of pretreatment protocols for the reduction of the immunogenicity of small bowel allografts. Copyright (C) 2000 S. Karger AG, Basel

Biomechanical analysis of the late approach and the take off in the indoor women’s long jump

Aim of the study was to provide evidence concerning the biomechanical parameters of contemporary Women’s long jump in indoor competition. The final six steps and the take-off of 11 jumps (6.88 ± 0.23 m) were recorded (panning camera; sampling frequency: 300 fps) in an indoor competition. The examined parameters were a) the step parameters, the percentage distribution of adjustment (ADJ%) and the inter-limb symmetry angle (θSYM) in the late approach, b) the joint angles and the take-off parameters. Pearson’s correlation analysis revealed that approach velocity (9.8 ± 0.3 m/s) was significantly correlated (r = .86, p = .001) with effective distance (6.96 ± 0.23 m). The largest ADJ% (57.6 %) was executed at the penultimate step which was 12.2 ± 2.8 % larger than the last step. An inter-limb difference was revealed for step frequency (t10 = 6.965, p < .001) due to the large asymmetry observed (θSYM = 5.54 deg). The knee angle of the push-off leg at take-off was 171.2 ± 4.7deg. Resultant velocity (8.3 ± 0.4 m/s), height (1.15 ± 0.05 m) and angle (20.7 ± 2.3 deg) of take-off significantly predicted effective distance (F3,7 = 12.671, p = .003, R2 = .844). The present findings are in reasonable agreement with previous research. Future studies should examine the possible reliance and asymmetry for the step parameters in the final approach

Random Exchange Disorder in the Spin-1/2 XXZ Chain

The one-dimensional XXZ model is studied in the presence of disorder in the Heisenberg Exchange Integral. Recent predictions obtained from renormalization group calculations are investigated numerically using a Lanczos algorithm on chains of up to 18 sites. It is found that in the presence of strong X-Y-symmetric random exchange couplings, a ``random singlet'' phase with quasi-long-range order in the spin-spin correlations persists. As the planar anisotropy is varied, the full zero-temperature phase diagram is obtained and compared with predictions of Doty and Fisher [Phys. Rev. B {\bf 45 }, 2167 (1992)].Comment: 9 pages + 8 plots appended, RevTex, FSU-SCRI-93-98 and ORNL/CCIP/93/1

Nature reappraisers, benefits for the environment: A model linking cognitive reappraisal, the “being away” dimension of restorativeness and eco-friendly behavior

In the last decades, an increasingly prominent role has been given to the motivational factors that can promote pro-environmental behavior. In this contribution, we focus on the role of the individual’s ability to shape the emotions originating from nature in engaging in pro-environmental behavior. In particular, we expect that an emotion regulation strategy as cognitive reappraisal should positively predict pro-environmental behavior, through enhanced perceived restorativeness attributed to the natural environment in terms of the experience of “being away.” One-hundred and fifteen visitors to an urban park (Parco Nord Milano) filled out a questionnaire including measures of cognitive reappraisal, the experience of “being away,” and pro-environmental behaviour while in the park. Results confirmed that cognitive reappraisal was positively and significantly related to pro-environmental behavior. Importantly, the indirect effect of cognitive reappraisal on pro-environmental behavior through the experience of “being away” was significant. Findings suggest the importance of implementing interventions aimed at promoting the habitual use of cognitive reappraisal to enhance the experience of “being away” and, thus, sustain pro-environmental behavior

Numerical renormalization-group study of spin correlations in one-dimensional random spin chains

We calculate the ground-state two-spin correlation functions of spin-1/2 quantum Heisenberg chains with random exchange couplings using the real-space renormalization group scheme. We extend the conventional scheme to take account of the contribution of local higher multiplet excitations in each decimation step. This extended scheme can provide highly accurate numerical data for large systems. The random average of staggered spin correlations of the chains with random antiferromagnetic (AF) couplings shows algebraic decay like $1/r^2$, which verifies the Fisher's analytic results. For chains with random ferromagnetic (FM) and AF couplings, the random average of generalized staggered correlations is found to decay more slowly than a power-law, in the form close to $1/\ln(r)$. The difference between the distribution functions of the spin correlations of the random AF chains and of the random FM-AF chains is also discussed.Comment: 14 pages including 8 figures, REVTeX, submitted to Physical Review

THE USE OF UPPER LIMB PROSTHESIS OPTIMIZES LONG JUMP APPROACH KINEMATICS: A CASE STUDY OF AN ELITE T47 ATHLETE

This study aimed to investigate approach run kinematics using an upper limb prosthesis. A European Τ47 long- and triple- jump champion with right upper-limb congenital deficiency was analyzed in simulated approach run-ups wearing prosthesis (PW) or not (NP). Two attempts in each condition were recorded (300 fps). Step characteristics and kinematic parameters were extracted for the deficient (DLS) and intact (HLS) sides with a 2D-DLT analysis during the early (EA) and late (LA) approach. Results revealed systematic asymmetry for step frequency and length in NP, with the latter reduced in PW. Horizontal velocity in both EA and LA was larger by 0.3 m/s in PW than NP. These results suggest that asymmetry of NP reduces approach run performance compared to PW

Chronic eccentric exercise and antioxidant supplementation: effects on lipid profile and insulin sensitivity

Eccentric exercise has been shown to exert beneficial effects in both lipid profile and insulin sensitivity. Antioxidant supplementation during chronic exercise is controversial as it may prevent the physiological training-induced adaptations. The aim of this study was to investigate: 1) the minimum duration of the eccentric exercise training required before changes on metabolic parameters are observed and 2) whether antioxidant supplementation during training would interfere with these adaptations. Sixteen young healthy men were randomized into the Vit group (1 g of vitamin C and 400 IU vitamin E daily) and the placebo (PL) group. Subjects received the supplementation for 9 weeks. During weeks 5-9 all participants went through an eccentric exercise training protocol consisting of two exercise sessions (5 sets of 15 eccentric maximal voluntary contractions) per week. Plasma triglycerides (TG), total cholesterol (TC), high density lipoprotein (HDL), low density lipoprotein (LDL), apolipoproteins (Apo A1, Apo B and Lpa) and insulin sensitivity (HOMA) were assessed before the supplementation (week 0), at weeks 5, 6, 7, 8 and 9. TG, TC and LDL were significantly lower compared to pre supplementation at both weeks 8 and 9 (P<0.05) in both groups. HDL was significantly elevated after 4 weeks of training (p < 0.005) in both groups. There was no effect of the antioxidant supplementation in any of the variables. There was no effect of either the training or the supplementation protocol in apolipoproteins levels and insulin sensitivity. A minimum duration of 3 weeks of eccentric exercise training is required before beneficial effects in lipid profile can be observed in healthy young men. Concomitant antioxidant supplementation does not interfere with the training-induced adaptations