Exact Monte Carlo time dynamics in many-body lattice quantum systems

On the base of a Feynman-Kac--type formula involving Poisson stochastic processes, recently a Monte Carlo algorithm has been introduced, which describes exactly the real- or imaginary-time evolution of many-body lattice quantum systems. We extend this algorithm to the exact simulation of time-dependent correlation functions. The techniques generally employed in Monte Carlo simulations to control fluctuations, namely reconfigurations and importance sampling, are adapted to the present algorithm and their validity is rigorously proved. We complete the analysis by several examples for the hard-core boson Hubbard model and for the Heisenberg model

Resonant, broadband and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths

Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximately 500 MW/cm2 peak power density, we predict third harmonic conversion efficiencies of approximately 1% in a silicon nanowire array, at nearly any desired UV or visible wavelength, including the range of negative dielectric constant. We also predict surface second harmonic conversion efficiencies of order 0.01%, depending on the electronic effective mass, bistable behavior of the signals as a result of a reshaped resonance, and the onset fifth order nonlinear effects. These remarkable findings, arising from the combined effects of nonlinear resonance dispersion, field localization, and phase-locking, could significantly extend the operational spectral bandwidth of silicon photonics, and strongly suggest that neither linear absorption nor skin depth should be motivating factors to exclude either semiconductors or metals from the list of useful or practical nonlinear materials in any spectral range.Comment: 12 pages, 4 figure

Avaliacao da eficiência de fungicidas no controle da cercosporiose (Cercospora zeae-maydis) na cultura do milho.

A cercosporiose do milho, causada pelo fungo Cercospora Zeae-maydis, é atualmente, no Brasil, uma das mais importantes doenças foliares dessa cultura, apresentando maior severidade de danos no sudoeste de Goiás. Este experimento foi conduzido em área de plantio direto de milho sobre milho, no município de Montividíu, ao, infectada com Cercospora zeae-maydis. O delineamento experimental foi o de blocos ao acaso, com 8 tratamentos em 4 repetições. Foi utilizado o híbrido simples Avant, de ciclo precoce. Os fungicidas foram aplicados mediante pulverizador manual pressurizado com 4 bicos pulverizadores. O volume de calda aplicado em cada parcela foi de I ,4 litros. Foram utilizados os seguintes fungicidas (g i.a.ha-1): propiconazole (100,0), propiconazole (125,0), difenoconazole (50,0), difenoconazole (75,0), azoxystrobin (50,0), azoxystrobin (75,0) e tebuconazole (200,0). Parcelas sem tratamento fungicida constituíram a testemunha. A primeira pulverização dos fungicidas foi realizada em plantas no estádio V8 (43 Dias Após o Plantio - DAP) e a segunda no estádio de pré_ emborrachamento (58 DAP). Aos 85 DAP, com plantas com espigas no estádio de grão pastoso, procedeu-se à avaliação dos sintomas foliares causados por Cercospora zeae-maydis, utilizando-se do seguinte esquema de notas: O =sem sintoma; 1 = poucas lesões nas folhas abaixo da espiga, nenhuma lesão acima; 2 = muitas lesões nas folhas abaixo da espiga, poucas lesões acima; 3 = severo desenvolvimento de lesões nas folhas abaixo da espiga, todas as folhas acima da espiga com lesões; 4 = todas as folhas com severo desenvolvimento de lesões, mas tecido verde ainda visível; 5 = todas as folhas secas e mortas. Os resultados obtidos mostram que os fungicidas propiconazole, difenoconazole, azoxystrobin e tebuconazole foram eficientes no controle da cercosporiose (Cercospora zeae-maydis) do milho e todos os tratamentos fungicida garantiram a produção de grãos de milho, sendo que a maior diferença percentual foi de 38,9% em relação à testemunha. Conclui-se que os fungicidas propiconazole, difenoconazole, azoxystrobin e tebuconazole são eficientes no controle da cercosporiose do milho causada por Cercospora zeae-maydis e que a aplicação destes produtos garantem significativamente a produção de grãos

Asymptotic Flatness in Rainbow Gravity

A construction of conformal infinity in null and spatial directions is constructed for the Rainbow-flat space-time corresponding to doubly special relativity. From this construction a definition of asymptotic DSRness is put forward which is compatible with the correspondence principle of Rainbow gravity. Furthermore a result equating asymptotically flat space-times with asymptotically DSR spacetimes is presented.Comment: 11 page

Robotic vs laparoscopic total mesorectal excision for rectal cancers: has a paradigm change occurred? A systematic review by updated meta-analysis

Aim The debate about the oncological adequacy, safety and efficiency of robotic vs laparoscopic total mesorectal excision for rectal cancers continues. Therefore, an updated, traditional and cumulative meta-analysis was performed with the aim of assessing the new evidence on this topic. Method A systematic search of the literature for data pertaining to the last 25 years was performed. Fixed- and random-effects models were used to cumulatively assess the accumulation of evidence over time. Results Patients with a significantly higher body mass index (BMI), tumours located approximately 1 cm further distally and more patients undergoing neoadjuvant therapy were included in the robotic total mesorectal excision (RTME) cohort compared with those in the laparoscopic total mesorectal excision (LTME) cohort [RTME, mean difference (MD) = 0.22 (0.07, 0.36), P = 0.005; LTME, MD = -0.97 (-1.57, 0.36), P < 0.002; OR = 1.47 (1.11, 1.93), P = 0.006]. Significantly lower conversion rates to open surgery were observed in the RTME cohort than in the LTME cohort [OR = 0.33 (0.24, 0.46), P < 0.001]. Operative time in the LTME cohort was significantly reduced (by 50 min) compared with the RTME cohort. Subgroup analysis of the three randomized controlled trials (RCTs) challenged all the significant results of the main analysis and demonstrated nonsignificant differences between the RTME cohort and LTME cohort. Conclusion Although the RTME cohort included patients with a significantly higher BMI, more distal tumours and more patients undergoing neoadjuvant therapy, this cohort demonstrated lower conversion rates to open surgery when compared with the LTME cohort. However, subgroup analysis of the RCTs demonstrated nonsignificant differences between the two procedures

Scaling Bounded Model Checking By Transforming Programs With Arrays

Bounded Model Checking is one the most successful techniques for finding bugs in program. However, model checkers are resource hungry and are often unable to verify programs with loops iterating over large arrays.We present a transformation that enables bounded model checkers to verify a certain class of array properties. Our technique transforms an array-manipulating (ANSI-C) program to an array-free and loop-free (ANSI-C) program thereby reducing the resource requirements of a model checker significantly. Model checking of the transformed program using an off-the-shelf bounded model checker simulates the loop iterations efficiently. Thus, our transformed program is a sound abstraction of the original program and is also precise in a large number of cases - we formally characterize the class of programs for which it is guaranteed to be precise. We demonstrate the applicability and usefulness of our technique on both industry code as well as academic benchmarks

Single - particle correlations in events with the total disintegration of nuclei

New experimental data on the behaviour of the single-particle two-dimensional correlation functions R versus Q (Q is the number of nucleons emitted from nuc- lei) and Ap (Ap is the mass of projectile nuclei) are presented in this paper. The interactions of protons, d, 4He and 12C nuclei with carbon nuclei (at a momentum of 4.2 A GeV/c) are considered.The values of R are obtained separately for pi minus mesons and protons.In so doing,the values of R are normalized so that -1=<R=<1.The value of R=0 corresponds to the case of the absence of corre- lations.It has been found that the Q- and Ap-dependence of R takes place only for weak correlations (R< 0.3).In the main (90 %),these correlations are con- nected with the variable pt and have a nonlinear character, that is the regi- ons with different characters of the Q-dependence of R are separated: there is a change of regimes in the Q-dependences of R.The correlations weaken with increasing Ap, and the variable R gets the least values of all the considered ones in 12CC interactions.Simultaneously with weakening the correlations in the region of large Q, the character of the Q-dependence of R changes.Comment: 17 pages, submitted to Phys. Rew.

Unitarity Bounds for Gauged Axionic Interactions and the Green-Schwarz Mechanism

We analyze the effective actions of anomalous models in which a four-dimensional version of the Green-Schwarz mechanism is invoked for the cancellation of the anomalies, and we compare it with those models in which gauge invariance is restored by the presence of a Wess-Zumino term. Some issues concerning an apparent violation of unitarity of the mechanism, which requires Dolgov-Zakharov poles, are carefully examined, using a class of amplitudes studied in the past by Bouchiat-Iliopoulos-Meyer (BIM), and elaborating on previous studies. In the Wess-Zumino case we determine explicitly the unitarity bound using a realistic model of intersecting branes (the Madrid model) by studying the corresponding BIM amplitudes. This is shown to depend significantly on the St\"uckelberg mass and on the coupling of the extra anomalous gauge bosons and allows one to identify Standard-Model-like regions (which are anomaly-free) from regions where the growth of certain amplitudes is dominated by the anomaly, separated by an inflection point which could be studied at the LHC. The bound can even be around 5-10 TeV's for a $Z'$ mass around 1 TeV and varies sensitively with the anomalous coupling. The results for the WZ case are quite general and apply to all the models in which an axion-like interaction is introduced as a generalization of the Peccei-Quinn mechanism, with a gauged axion.Comment: 50 pages, 28 figure

Acute mesenteric ischaemia in refractory shock on veno-arterial extracorporeal membrane oxygenation

Background: Acute mesenteric ischaemia is a severe complication in critically ill patients, but has never been evaluated in patients on veno-arterial extracorporeal membrane oxygenation (V-A ECMO). This study was designed to determine the prevalence of mesenteric ischaemia in patients supported by V-A ECMO and to evaluate its risk factors, as well as to appreciate therapeutic modalities and outcome. Methods: In a retrospective single centre study (January 2013 to January 2017), all consecutive adult patients who underwent V-A ECMO were included, with exclusion of those dying in the first 24 hours. Diagnosis of mesenteric ischaemia was performed using digestive endoscopy, computed tomography scan or first-line laparotomy. Results: One hundred and fifty V-A ECMOs were implanted (65 for post-cardiotomy shock, 85 for acute cardiogenic shock, including 39 patients after refractory cardiac arrest). Overall, median age was 58 (48-69) years and mortality 56%. Acute mesenteric ischaemia was suspected in 38 patients, with a delay of four (2-7) days after ECMO implantation, and confirmed in 14 patients, that is, a prevalence of 9%. Exploratory laparotomy was performed in six out of 14 patients, the others being too unstable to undergo surgery. All patients with mesenteric ischaemia died. Independent risk factors for developing mesenteric ischaemia were renal replacement therapy (odds ratio (OR) 4.5, 95% confidence interval (CI) 1.3-15.7, p=0.02) and onset of a second shock within the first five days (OR 7.8, 95% CI 1.5-41.3, p=0.02). Conversely, early initiation of enteral nutrition was negatively associated with mesenteric ischaemia (OR 0.15, 95% CI 0.03-0.69, p=0.02). Conclusions: Acute mesenteric ischaemia is a relatively frequent but dramatic complication among patients on V-A ECMO