Real time evolution using the density matrix renormalization group

We describe an extension to the density matrix renormalization group method incorporating real time evolution into the algorithm. Its application to transport problems in systems out of equilibrium and frequency dependent correlation functions is discussed and illustrated in several examples. We simulate a scattering process in a spin chain which generates a spatially non-local entangled wavefunction.Comment: 4 pages, 4 eps figures, some minor corrections in text and Eq.(3

Minimum stress and pore fluid pressure in sedimentary basins

Leak-off pressures (LOPs) recorded during leak-off tests (LOTs) conducted down boreholes are often used to estimate the magnitude of the minimum stress (usually assumed to be horizontal – S(_h)) in the subsurface. However, the reliability of these tests has previously been questioned in the literature and the accuracy of the data obtained from them has been in doubt. Using original LOT data from Mid-Norway, this study has shown that through stringent quality control, good LOT data can be used to accurately constrain the magnitude of S(_h). Knowledge of the relationship between in-situ stress and pore pressures (Pp) in basins provides insights into their structure as well as having implications for well design and drilling safety. Using stress-depth plots to display S(_h) measurements from Mid-Norway and six further basins from around the world reveals a variability in the magnitude of Sh at all depths. Analyses show that rock mechanical properties or differences in the way LOTs are performed cannot explain this variability. Separate analysis of extended leak-off test (XLOT) data from Mid-Norway shows that variability in the magnitude of the LOP (most often used to calculate S(_h)) is inherent in the testing procedure. This inherence suggests either the variations in Sh are real (they represent basin heterogeneities) or that they result from a combination or rock mechanical and/or pumping pressure test parameters. Further use of multiple cycle XLOTs shows that using LOPs and instantaneous shut-in pressures (ISIPs) to calculate S(_h) produces similar results. Considering re-opening cycles of tests and those tests from greater depths shows the difference between the magnitude of Sh calculated using the LOP and ISIP is reduced. These same high quality data have been used to calculate the magnitude of the three principal stress from Mid-Norway and show the contemporary stress situation to be S(_h)<S(_v)<S(_H).Compilations of S(_h) and P(_p) have also been used to calculate the lower bound to LOPs and the upper limit to P(_p) as means of predicting Sh. Results show that using the lower bound to estimate the maximum P(_p) (or the upper limit to estimate S(_h)) will lead to large errors within normally pressured zones but successful estimates at overpressured depths. Analyses also show that there is no systematic relationship between the magnitude of the lower bound to LOPs and the contemporary stress situation. The S(_h) and P(_p) data were normalised to a "hypothetical unconstrained basiri' and/or depth to investigate pore pressure in-situ stress coupling and quantify the change in S(_h) with overpressure. Results show that coupling can be inferred in three of the seven basins studied. Poro-elasticity or frictional limits to stress are the most likely coupling mechanisms because regional S(_h) magnitudes do not relate to tectonic regime. Coupling is not inferred for Mid-Norway. An explanation for the lack of coupling is the late timing of overpressure following normal compaction of the rocks. It is suggested that "inflationary mechanism" overpressures produce lower ∆S(_h)/ ∆P(_p) values than overpressures that developed synchronous with burial. Using the poro-elasticity equation to back-calculate the Poisson's ratio (v) of the rocks reveals high values thus establishing a relationship between high v and higher levels of compaction

Bringing Pankaj Ghemawat to Africa: Measuring African economic integration

A wealth of literature dealing with trade liberalisation, capital market liberalisation, labour mobility and related issues concerning globalisation asserts that economies that are more integrated with the global economy and, more specifically with their neighbours, tend to enjoy higher sustained levels of growth. Empirical evidence with solid quantitative findings recently conducted by Pankaj Ghemawat has confirmed that more ‘open and connected’ economies display higher rates of economic growth, higher per capita income levels and greater levels of human welfare. Against this backdrop, it is notable that the available evidence – whilst incomplete – suggests that African economies are amongst the least integrated in the world. Given that integration and connectedness matter, and that there are material gaps in the evaluation of integration for African economies, it is important to develop better measures of African economies’ connectedness with their neighbours and with the world, how this connectedness is evolving and establish more comprehensive and robust means of economic integration compared to those historically available. Using Ghemawat’s framework, which measures flows of trade, capital, information and people (TCIP) to determine connectedness, we develop the Visa Africa integration index to provide a more comprehensive and detailed gauge of economic integration for 11 African countries in three clusters: East Africa, West Africa and Southern Africa. The index results suggest that African economies are emerging off a modest base, with some economies demonstrating progressive structural improvements toward higher levels of integration with their respective regions and the world. East Africa, in particular, shows signs of rising connectedness over the survey period. The index also illustrates that some countries are more integrated globally than regionally and vice versa, which is important information for policy makers toward improving deeper and broader integration in their respective regions. The index builds on previous research in the broad area of integration and helps us better understand the challenges and opportunities presented by Africa’s economic changes and some of the implications for economic growth.http://www.sajems.orgam2016Gordon Institute of Business Science (GIBS

Explaining Support for Animal Rights: A Comparison of Two Recent Approaches to Humans, Nonhuman Animals, and Postmodernity

Questions on "animal rights" in a cross-national survey conducted in 1993 provide an opportunity to compare the applicability to this issue of two theories of the socio-political changes summed up in "postmodernity": Inglehart's (1997) thesis of "postmaterialist values" and Franklin's (1999) synthesis of theories of late modernity. Although Inglehart seems not to have addressed human-nonhuman animal relations, it is reasonable to apply his theory of changing values under conditions of "existential security" to "animal rights." Inglehart's postmaterialism thesis argues that new values emerged within specific groups because of the achievement of material security. Although emphasizing human needs, they shift the agenda toward a series of lifestyle choices that favor extending lifestyle choices, rights, and environmental considerations. Franklin's account of nonhuman animals and modern cultures stresses a generalized "ontological insecurity." Under postmodern conditions, changes to core aspects of social and cultural life are both fragile and fugitive. As neighborhood, community, family, and friendship relations lose their normative and enduring qualities, companion animals increasingly are drawn in to those formerly exclusive human emotional spaces. With a method used by Inglehart and a focus in countries where his postmaterialist effects should be most evident, this study derives and tests different expectations from the theories, then tests them against data from a survey supporting Inglehart's theory. His theory is not well supported. We conclude that its own anthropocentrism limits it and that the allowance for hybrids of nature-culture in Franklin's account offers more promise for a social theory of animal rights in changing times

Monolithically integrated selectable repetition-rate laser diode source of picosecond optical pulses.

We describe the characterization of a monolithically integrated photonic device for short pulse generation featuring a mode-locked laser diode, a Mach-Zehnder modulator (MZM), and a semiconductor optical amplifier (SOA). The integrated device is designed for fabrication by a generic foundry scheme with a view to ease of design, testing, and manufacture. Trains of 6.8 ps pulses are generated at repetition rates that are electronically switchable from 14 GHz to 109 MHz. The SOA boosts the peak power by 7.4 dB, and the pulses are compressible to 2.4 ps by dispersion compensation using single-mode telecommunications fiber.This research leading to these results has received support from the UK EPSRC COPOS award EP/H022384/1 and from the European Commission’s Seventh Framework Programme FP7/2007-2013 under grant agreement NMP 228839 EuroPIC.This is the author accepted manuscript. The final published version can be found on the publisher's website at: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-14-414

Finite Temperature Density Matrix Renormalization using an enlarged Hilbert space

We apply a generalization of the time-dependent DMRG to study finite temperature properties of several quantum spin chains, including the frustrated $J_1-J_2$ model. We discuss several practical issues with the method, including use of quantum numbers and finite size effects. We compare with transfer-matrix DMRG, finding that both methods produce excellent results.Comment: 4 pages and 4 figure

Evidence of questionable research practices in clinical prediction models

Background Clinical prediction models are widely used in health and medical research. The area under the receiver operating characteristic curve (AUC) is a frequently used estimate to describe the discriminatory ability of a clinical prediction model. The AUC is often interpreted relative to thresholds, with “good” or “excellent” models defined at 0.7, 0.8 or 0.9. These thresholds may create targets that result in “hacking”, where researchers are motivated to re-analyse their data until they achieve a “good” result. Methods We extracted AUC values from PubMed abstracts to look for evidence of hacking. We used histograms of the AUC values in bins of size 0.01 and compared the observed distribution to a smooth distribution from a spline. Results The distribution of 306,888 AUC values showed clear excesses above the thresholds of 0.7, 0.8 and 0.9 and shortfalls below the thresholds. Conclusions The AUCs for some models are over-inflated, which risks exposing patients to sub-optimal clinical decision-making. Greater modelling transparency is needed, including published protocols, and data and code sharing