Quantum Phase Transitions and the Extended Coupled Cluster Method

We discuss the application of an extended version of the coupled cluster method to systems exhibiting a quantum phase transition. We use the lattice O(4) non-linear sigma model in (1+1)- and (3+1)-dimensions as an example. We show how simple predictions get modified, leading to the absence of a phase transition in (1+1) dimensions, and strong indications for a phase transition in (3+1) dimensions

Analysis of No-Difference Findings in Evaluation Research

Conclusions of no difference are becoming increasingly important in evaluation research. We delineate three major uses of no-difference findings and analyze their meanings. (1) No-differ ence findings in randomized experiments can be interpreted as support for conclusions of the absence of a meaningful treatment effect, but only if the proper analytic methods are used. (2) Statistically based conclusions in quasi-experiments do not allow causal statements about the treatment impact but do provide a metric to judge the size of the resulting difference. (3) Using no-difference findings to conclude equivalence on control variables is inefficient and potentially misleading. The final section of the article presents alternative methods by which conclusions of no difference may be supported when applicable. These methods include the use of arbitrarily high alpha levels, interval estimation, and power analysis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67182/2/10.1177_0193841X8901300604.pd

Supplemental Release Limits for the Directed Reuse of Steel in Road Barriers and Lead in Shielding Products by the Department of Energy

The DOE National Center of Excellence for Metals Recycle (NMR) proposes to define and implement a complex-wide directed reuse strategy for surplus radiologically impacted lead (Pb) and steel as part of the U.S. Department of Energy's commitment to the safe and cost-effective recycle or reuse of excess materials and equipment across the DOE complex. NMR will, under this proposal, act on behalf of the DOE Office of Environmental Management, Office of Technical Program Integration (specifically EM-22), as the Department's clearinghouse for DOE surplus lead, steel and products created from these materials by developing and maintaining a cost-effective commercially-based contaminated lead and steel recycle program. It is NMR's intention, through this directed reuse strategy, to mitigate the adverse environmental and economic consequences of managing surplus lead and steel as a waste within the complex. This approach promotes the safe and cost-effective reuse of scrap metals in support of the Department's goals of resource utilization, energy conservation, pollution prevention and waste minimization. This report discusses recommendations for supplemental radiological release limits for the directed reuse of contaminated lead and steel by the DOE within the nuclear industry. The limits were originally selected from the American National Standards Institute and Health Physics Society standard N13.12 titled ''Surface and Volume Radioactivity Standards for Clearance'' (Health Physics Society, 1999) but were subsequently modified as a result of application-specific issues. Both the health and measurement implications from the adoption and use of the limits for directed reuse scenarios are discussed within this report

Statistical Mechanics of Nonuniform Magnetization Reversal

The magnetization reversal rate via thermal creation of soliton pairs in quasi-1D ferromagnetic systems is calculated. Such a model describes e.g. the time dependent coercivity of elongated particles as used in magnetic recording media. The energy barrier that has to be overcome by thermal fluctuations corresponds to a soliton-antisoliton pair whose size depends on the external field. In contrast to other models of first order phase transitions such as the phi^4 model, an analytical expression for this energy barrier is found for all values of the external field. The magnetization reversal rate is calculated using a functional Fokker-Planck description of the stochastic magnetization dynamics. Analytical results are obtained in the limits of small fields and fields close to the anisotropy field. In the former case the hard-axis anisotropy becomes effectively strong and the magnetization reversal rate is shown to reduce to the nucleation rate of soliton-antisoliton pairs in the overdamped double sine-Gordon model. The present theory therefore includes the nucleation rate of soliton-antisoliton pairs in the double sine-Gordon chain as a special case. These results demonstrate that for elongated particles, the experimentally observed coercivity is significantly lower than the value predicted by the standard theories of N\'eel and Brown.Comment: 21 pages RevTex 3.0 (twocolumn), 6 figures available on request, to appear in Phys Rev B, Dec (1994

The self-consistent bounce: an improved nucleation rate

We generalize the standard computation of homogeneous nucleation theory at zero temperature to a scenario in which the bubble shape is determined self-consistently with its quantum fluctuations. Studying two scalar models in 1+1 dimensions, we find the self-consistent bounce by employing a two-particle irreducible (2PI) effective action in imaginary time at the level of the Hartree approximation. We thus obtain an effective single bounce action which determines the rate exponent. We use collective coordinates to account for the translational invariance and the growth instability of the bubble and finally present a new nucleation rate prefactor. We compare the results with those obtained using the standard 1-loop approximation and show that the self-consistent rate can differ by several orders of magnitude.Comment: 28 pages, revtex, 7 eps figure

Thermodynamic properties of the periodic Anderson model:X-boson treatment

We study the specific dependence of the periodic Anderson Model (PAM) in the limit of $U=\infty$ employing the X-boson treatment in two fifferent regimes of the PAM: the heavy fermion Kondo (HF-K) and the heavy fermion local magnetic regime (HF-LMM). We obtain a multiple peak structure for the specific heat in agreement with experimental results as well as the increase of the electronic effective mass at low temperatures associated with the HF-K regime. The entropy per site at low T tends to zero in the HF-K regime, corresponding to a singlet ground state, and it tends to $k_{B}ln(2)$ in the HF-LMM, corresponding to a doublet ground state at each site. The linear coefficient $\gamma(T)=C_{v}/T$ of the specific heat qualitatively agrees with the experimental results obtained for differents materials in the two regimes considered here.Comment: 9 pages, 14 figure

Thermal Decay of the Cosmological Constant into Black Holes

We show that the cosmological constant may be reduced by thermal production of membranes by the cosmological horizon, analogous to a particle ``going over the top of the potential barrier", rather than tunneling through it. The membranes are endowed with charge associated with the gauge invariance of an antisymmetric gauge potential. In this new process, the membrane collapses into a black hole, thus the net effect is to produce black holes out of the vacuum energy associated with the cosmological constant. We study here the corresponding Euclidean configurations ("thermalons"), and calculate the probability for the process in the leading semiclassical approximation.Comment: 14 pages, 6 figures. Minor correction

One-loop corrections to the metastable vacuum decay

We evaluate the one-loop prefactor in the false vacuum decay rate in a theory of a self interacting scalar field in 3+1 dimensions. We use a numerical method, established some time ago, which is based on a well-known theorem on functional determinants. The proper handling of zero modes and of renormalization is discussed. The numerical results in particular show that quantum corrections become smaller away from the thin-wall case. In the thin-wall limit the numerical results are found to join into those obtained by a gradient expansion.Comment: 31 pages, 7 figure

Combination therapy with an ACE inhibitor and an angiotensin receptor blocker for diabetic nephropathy - a meta-analysis

WSTĘP. Inhibitory konwertazy angiotensyny (ACEI) i blokery receptora angiotensyny (ARB) zapobiegają progresji nefropatii cukrzycowej (DN). Wyniki badań sugerują, że połączenie układu renina-angiotensyna-aldosteron (RAAS) i czynników hamujących działa addytywnie w procesie leczenia DN. Ponieważ badania te obejmowały niewielkie grupy chorych, autorzy niniejszej pracy przeprowadzili metaanalizę prób dotyczących leczenia skojarzonego DN. METODY. Badania do metaanalizy wybrano na podstawie baz danych MEDLINE, EMBASE, CINAHL i Cochrane. Włączono wszystkie próby dotyczące skojarzonego leczenia za pomocą ACEI i ARB. Głównym punktem końcowym było dobowe wydalanie białka z moczem, a dodatkowe punkty końcowe obejmowały: wartości ciśnienia tętniczego, stężenia potasu we krwi i współczynnika przesączania kłębuszkowego (GFR). WYNIKI. W 10 włączonych do analizy badaniach 156 chorych otrzymało ACEI i ARB, a 159 jedynie ACEI. Większość badań trwało 8-12 tygodni. U osób leczonych ACEI i ARB uzyskano zmniejszenie proteinurii (p = 0,01), co wiązało się ze znaczną statystyczną heterogenicznością (p = 0,005). Terapia ACEI i ARB była związana ze zmniejszeniem GFR [3,87 ml/min (7,32-0,42); p = 0,03] i tendencją do wzrostu stężenia kreatyniny w surowicy (6,86 umol/l 95% CI -0,76-13,73; p = 0,09). Stężenie potasu zwiększyło się o 0,2 (0,08-0,32) mmol/l (p < 0,01) u chorych leczonych ACEI i ARB. Skurczowe i rozkurczowe ciśnienie krwi obniżyło się odpowiednio o 5,2 mm Hg (2,1-8,4) (p < 0,01) i 5,3 mm Hg (2,2-8,4) (p < 0,01). WNIOSKI. Wyniki metaanalizy sugerują, że łączne stosowanie ACEI + ARB w większym stopniu zmniejsza 24-godzinne wydalanie białka z moczem niż przyjmowanie jedynie ACEI. Korzystne efekty terapii skojarzonej są wynikiem niewielkiego wpływu leków na GFR, stężenie kreatyniny i potasu w surowicy oraz ciśnienie tętnicze. Rezultaty te należy interpretować ostrożnie, ponieważ większość analizowanych badań charakteryzowała się krótkim czasem obserwacji, a w kilku długoterminowych próbach (12 miesięcy) nie wykazano korzystnego wpływu leczenia.AIMS. Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) prevent the progression of diabetic nephropathy (DN). Studies suggest that combination renin-angiotensin-aldosterone system (RAAS)-inhibiting therapy provides additive benefit in DN. However, these studies are small in size. We performed a meta-analysis of studies investigating combination therapy for DN. METHODS. Studies were identified through a search of MEDLINE, EMBASE, CINAHL and the Cochrane Database. All trials involving combined ACEI and ARB for slowing progression of DN were included. The primary end point was 24- Blood pressure, serum potassium and glomerular filtration rate (GFR) were secondary end points. RESULTS. In the 10 included trials, 156 patients received ACEI + ARB and 159 received ACEI only. Most studies were 8&#8211;12 weeks in duration. Proteinuria was reduced with ACEI + ARB (p = 0.01). This was associated with significant statistical heterogeneity (p = 0.005). ACEI + ARB was associated with a reduction in GFR [3.87 ml/min (7.32-0.42); p = 0.03] and a trend towards an increase in serum creatinine (6.86 umol/l 95% CI: -0.76-13.73; p = 0.09). Potassium was increased by 0.2 (0.08-0.32) mmol/l (p < 0.01) with ACEI + ARB. Systolic and diastolic blood pressure were reduced by 5.2 (2.1-8.4) mm Hg (p < 0.01) and 5.3 (2.2-8.4) mm Hg (p < 0.01), respectively. CONCLUSIONS. This meta-analysis suggests that ACEI + + ARB reduces 24-h proteinuria to a greater extent than ACEI alone. This benefit is associated with small effects on GFR, serum creatinine, potassium and blood pressure. These results should be interpreted cautiously as most of the included studies were of short duration and the few long-term studies (12 months) have not demonstrated benefi