Matrix product state comparison of the numerical renormalization group and the variational formulation of the density matrix renormalization group

Wilson's numerical renormalization group (NRG) method for solving quantum impurity models yields a set of energy eigenstates that have the form of matrix product states (MPS). White's density matrix renormalization group (DMRG) for treating quantum lattice problems can likewise be reformulated in terms of MPS. Thus, the latter constitute a common algebraic structure for both approaches. We exploit this fact to compare the NRG approach for the single-impurity Anderson model to a variational matrix product state approach (VMPS), equivalent to single-site DMRG. For the latter, we use an ``unfolded'' Wilson chain, which brings about a significant reduction in numerical costs compared to those of NRG. We show that all NRG eigenstates (kept and discarded) can be reproduced using VMPS, and compare the difference in truncation criteria, sharp vs. smooth in energy space, of the two approaches. Finally, we demonstrate that NRG results can be improved upon systematically by performing a variational optimization in the space of variational matrix product states, using the states produced by NRG as input.Comment: 19 pages, 14 figure

Nilpotence varieties

We consider algebraic varieties canonically associated with any Lie superalgebra, and study them in detail for super-Poincaré algebras of physical interest. They are the locus of nilpotent elements in (the projectivized parity reversal of) the odd part of the algebra. Most of these varieties have appeared in various guises in previous literature, but we study them systematically here, from a new perspective: As the natural moduli spaces parameterizing twists of a super-Poincaré-invariant physical theory. We obtain a classification of all possible twists, as well as a systematic analysis of unbroken symmetry in twisted theories. The natural stratification of the varieties, the identification of strata with twists, and the action of Lorentz and R-symmetry are emphasized. We also include a short and unconventional exposition of the pure spinor superfield formalism, from the perspective of twisting, and demonstrate that it can be applied to construct familiar multiplets in four-dimensional minimally supersymmetric theories. In all dimensions and with any amount of supersymmetry, this technique produces BRST or BV complexes of supersymmetric theories from the Koszul complex of the maximal ideal over the coordinate ring of the nilpotence variety, possibly tensored with any equivariant module over that coordinate ring. In addition, we remark on a natural connection to the Chevalley–Eilenberg complex of the supertranslation algebra, and give two applications related to these ideas: a calculation of Chevalley–Eilenberg cohomology for the (2, 0) algebra in six dimensions, and a degenerate BV complex encoding the type IIB supergravity multiplet

Ancilla-assisted sequential approximation of nonlocal unitary operations

We consider the recently proposed "no-go" theorem of Lamata et al [Phys. Rev. Lett. 101, 180506 (2008)] on the impossibility of sequential implementation of global unitary operations with the aid of an itinerant ancillary system and view the claim within the language of Kraus representation. By virtue of an extremely useful tool for analyzing entanglement properties of quantum operations, namely, operator-Schmidt decomposition, we provide alternative proof to the "no-go" theorem and also study the role of initial correlations between the qubits and ancilla in sequential preparation of unitary entanglers. Despite the negative response from the "no-go" theorem, we demonstrate explicitly how the matrix-product operator(MPO) formalism provides a flexible structure to develop protocols for sequential implementation of such entanglers with an optimal fidelity. The proposed numerical technique, that we call variational matrix-product operator (VMPO), offers a computationally efficient tool for characterizing the "globalness" and entangling capabilities of nonlocal unitary operations.Comment: Slightly improved version as published in Phys. Rev.

Observer weighting of interaural cues in positive and negative envelope slopes of amplitude-modulated waveforms

The auditory system can encode interaural delays in highpass-filtered complex sounds by phase locking to their slowly modulating envelopes. Spectrotemporal analysis of interaurally time-delayed highpass waveforms reveals the presence of a concomitant interaural level cue. The current study systematically investigated the contribution of time and concomitant level cues carried by positive and negative envelope slopes of a modified sinusoidally amplitude-modulated (SAM) high-frequency carrier. The waveforms were generated from concatenation of individual modulation cycles whose envelope peaks were extended by the desired interaural delay, allowing independent control of delays in the positive and negative modulation slopes. In experiment 1, thresholds were measured using a 2-interval forced-choice adaptive task for interaural delays in either the positive or negative modulation slopes. In a control condition, thresholds were measured for a standard SAM tone. In experiment 2, decision weights were estimated using a multiple-observation correlational method in a single-interval forced-choice task for interaural delays carried simultaneously by the positive, and independently, negative slopes of the modulation envelope. In experiment 3, decision weights were measured for groups of 3 modulation cycles at the start, middle, and end of the waveform to determine the influence of onset dominance or recency effects. Results were consistent across experiments: thresholds were equal for the positive and negative modulation slopes. Decision weights were positive and equal for the time cue in the positive and negative envelope slopes. Weights were also larger for modulations cycles near the waveform onset. Weights estimated for the concomitant interaural level cue were positive for the positive envelope slope and negative for the negative slope, consistent with exclusive use of time cues.We thank Virginia M. Richards and Bruce G. Berg for helpful discussions. We also thank Brian C. J. Moore and an anonymous reviewer for their insightful comments on an earlier draft of the manuscript. Work supported by grants from the National Science Council, Taiwan NSC 98-2410-H-008-081-MY3 and NIH R01DC009659

The de-bordering process in urban landscapes: a land use and land cover analysis of a Pyrenean border region - the Central area of the cross-border Catalan space

An einer politischen Grenze kommt es zu Auswirkungen auf die Landschaft - als Folge des Nebeneinanders von zwei politischen und wirtschaftlichen Systemen und auch als Ergebnis wirtschaftlicher Chancen. Diese Auswirkungen hängen von der Art der Grenzen und ihrer Öffnung ab. Im Beitrag wird die Landschaftsentwicklung auf beiden Seiten der Grenze im Zentralbereich der katalanischen Grenzregion verglichen. Die Studie untersucht die Landnutzung in drei Zeiträume von den 1950er Jahren bis 2009. In Bezug zur Umwandlung der Stadtlandschaft werden verschiedene räumliche Strategien, die von den Gemeinden auf beiden Seiten der Grenze entwickelt wurden, durch Vergleich der Landschaft bewertet. Beurteilt wird, wie der Verlust der Grenze des Franco-Spaniens die Dynamik urbanen Raums beeinflusst und verwandelt hat, insbesondere in den Gemeinden Le Boulou und La Jonquera. Da die Grenze noch immer zwei unterschiedliche politische Verwaltungen trennt, ist es wichtig, vorhandene Landschaftsunterschiede zu beobachten. Wird die Öffnung der Grenze für Menschen und Güter die urbane Veränderung in Verbindung mit den durch die Grenze geschaffenen wirtschaftlichen Möglichkeiten beschleunigen? Nehmen durch das Ende der Abschottungswirkung der Grenze die Veränderungen im Stadtbild zu? Erste Ergebnisse bestätigen das. Sie zeigen auch tiefere Veränderungen des urbanen Raums an der südlichen Seite der Grenze aufgrund des Nebeneinanders unterschiedlicher politischer und wirtschaftlicher Systeme im Zusammenhang von offener Grenze und Globalisierung. Abschließende Ergebnisse weisen auch darauf hin, dass politische Entscheidungen - insbesondere auf lokaler Ebene getroffene - erhebliche Auswirkungen auf die Dynamik der Landschaft haben.The presence of a political border in a region has an impact in the landscape. Implications of the boundary on border landscapes could be the consequence of the juxtaposition of two political and economic systems and also the result of economic opportunities offered by borders. These impacts depend on the nature of borders and their opening in the EU might change border’s impacts upon landscapes. In this research landscape evolution on either side of the border in the central area of the Cross-Border Catalan Space is compared. The study is based on the land use and analyses three periods in time from the 1950s until 2009. Focusing on the urban landscape transformation, different territorial strategies developed by the municipalities located in each side of the border are evaluated through landscape comparison. Furthermore, it assesses how the loss of function of the Franco-Spanish border has affected and transformed the urban landscape dynamics, especially in Le Boulou (France) and La Jonquera (Spain) municipalities. Given that the border is still the limit between two different political administrations, it is important to observe the existence of landscape differences. Will the border’s opening to the flow of people and goods accelerate the urban transformation related to economic opportunities generated by the border? In other words, is the end of the border's breaking effect going to increase urban landscape transformations? Initial results show an increase of the urban landscape transformation closely related to the de-bordering process. They also demonstrate deeper urban landscape changes in the southern side of the boundary due to the juxtaposition of different legal and economic systems in an open border and globalised context. Final results also indicate that political decisions have a considerable impact over the landscape dynamics, particularly in those taken at the local level

Detection of sinusoidal amplitude modulation in logarithmic frequency sweeps across wide regions of the spectrum

a b s t r a c t Many natural sounds such as speech contain concurrent amplitude and frequency modulation (AM and FM), with the FM components often in the form of directional frequency sweeps or glides. Most studies of modulation coding, however, have employed one modulation type in stationary carriers, and in cases where mixed-modulation sounds have been used, the FM component has typically been confined to an extremely narrow range within a critical band. The current study examined the ability to detect AM signals carried by broad logarithmic frequency sweeps using a 2-alternative forced-choice adaptive psychophysical design. AM-detection thresholds were measured as a function of signal modulation rate and carrier sweep frequency region. Thresholds for detection of AM in a sweep carrier ranged from À8 dB for an AM rate of 8 Hz to À30 dB at 128 Hz. Compared to thresholds obtained for stationary carriers (pure tones and filtered Gaussian noise), detection of AM carried by frequency sweeps substantially declined at low (12 dB at 8 Hz) but not high modulation rates. Several trends in the data, including sweep-versus stationary-carrier threshold patterns and effects of frequency region were predicted from a modulation filterbank model with an envelope-correlation decision statistic

Personality Traits of Mentally Disordered Males Who Committed Homicide

Background: The relationship between personality traits and criminal behavior has not been sufficiently investigated. This study was done to determine the personality traits in a group of criminals who have committed homicide.Methods: This study was conducted to compare the personality traits in three groups of people in Tehran during 2014. The statistical population was examined 3 communities; first, forensic psychiatric patients; Second, people who accused homicide without psychiatric diagnosis; and, matched group (with no diagnosis and crime). The study sample included 121 males; they have been divided into 3 groups: psychiatric patients who have committed homicide (n=41), murderers without any major psychiatric disorder (n=40) and control group which includes non-committed and non-patient (n=40). The cases were evaluated by a short form of Neo questionnaire.Results: There was a significant difference between the groups in terms of personality traits, which included neurosis, extroversion, agreeableness and conscientiousness. The most significant difference was in extroversion and conscientiousness variables. Psychiatric patients’ committed homicide showed higher scores than those of non-patient and the control group. Psychiatric patients had lower scores in extroversion, agreeableness and conscientiousness characteristics in comparison with the other two groups.Conclusion: Psychiatric patients who have committed homicide have more Irascible traits. Non-patient cases who committed homicide have a tendency to introspection and egocentrism and they are socially compatible in comparison with patient groups. These subjects are among dispassionate ones. The results of this study failed to demonstrate a significant difference between non-patient cases who have committed homicide and the control group

Who will use pre-exposure prophylaxis (PrEP) and why?: Understanding PrEP awareness and acceptability amongst men who have sex with men in the UK – a mixed methods study

Background: Recent clinical trials suggest that pre-exposure prophylaxis (PrEP) may reduce HIV transmission by up to 86% for men who have sex with men (MSM), whilst relatively high levels of PrEP acceptability have been reported to date. This study examines PrEP awareness amongst sub-groups of MSM communities and acceptability amongst MSM in a low prevalence region (Scotland, UK), using a mixed methods design. Methods: Quantitative surveys of n = 690 MSM recruited online via social and sociosexual media were analysed using descriptive statistics and multivariate logistic regression. In addition, n = 10 in-depth qualitative interviews with MSM were analysed thematically. Results: Under one third (29.7%) of MSM had heard of PrEP, with awareness related to living in large cities, degree level education, commercial gay scene use and reporting an HIV test in the last year. Just under half of participants (47.8%) were likely to use PrEP if it were available but there was no relationship between PrEP acceptability and previous PrEP awareness. Younger men (18–25 years) and those who report higher risk UAI were significantly more likely to say they would use PrEP. Qualitative data described specific PrEP scenarios, illustrating how risk, patterns of sexual practice and social relationships could affect motivation for and nature of PrEP use. Conclusion: These findings suggest substantial interest PrEP amongst MSM reporting HIV risk behaviours in Scotland. Given the Proud results, there is a strong case to investigate PrEP implementation within the UK. However, it appears that disparities in awareness have already emerged along traditional indicators of inequality. Our research identifies the need for comprehensive support when PrEP is introduced, including a key online component, to ensure equity of awareness across diverse MSM communities (e.g. by geography, education, gay scene use and HIV proximity), as well as to responding to the diverse informational and sexual health needs of all MSM communities