A DMRG Study of Low-Energy Excitations and Low-Temperature Properties of Alternating Spin Systems

We use the density matrix renormalization group (DMRG) method to study the ground and low-lying excited states of three kinds of uniform and dimerized alternating spin chains. The DMRG procedure is also employed to obtain low-temperature thermodynamic properties of these systems. We consider a 2N site system with spins $s_1$ and $s_2$ alternating from site to site and interacting via a Heisenberg antiferromagnetic exchange. The three systems studied correspond to $(s_1 ,s_2 )$ being equal to $(1,1/2),(3/2,1/2)$ and $(3/2,1)$; all of them have very similar properties. The ground state is found to be ferrimagnetic with total spin $s_G =N(s_1 - s_2)$. We find that there is a gapless excitation to a state with spin $s_G -1$, and a gapped excitation to a state with spin $s_G +1$. Surprisingly, the correlation length in the ground state is found to be very small for this gapless system. The DMRG analysis shows that the chain is susceptible to a conditional spin-Peierls instability. Furthermore, our studies of the magnetization, magnetic susceptibility $\chi$ and specific heat show strong magnetic-field dependences. The product $\chi T$ shows a minimum as a function of temperature T at low magnetic fields; the minimum vanishes at high magnetic fields. This low-field behavior is in agreement with earlier experimental observations. The specific heat shows a maximum as a function of temperature, and the height of the maximum increases sharply at high magnetic fields. Although all the three systems show qualitatively similar behavior, there are some notable quantitative differences between the systems in which the site spin difference, $|s_1 - s_2|$, is large and small respectively.Comment: 16 LaTeX pages, 13 postscript figure

On effects of regular S=1 dilution of S=1/2 antiferromagnetic Heisenberg chains by a quantum Monte Carlo simulation

The effects of regular S=1 dilution of S=1/2 isotropic antiferromagnetic chain are investigated by the quantum Monte Carlo loop/cluster algorithm. Our numerical results show that there are two kinds of ground-state phases which alternate with the variation of $S^1=1$ concentration. When the effective spin of a unit cell is half-integer, the ground state is ferrimagnetic with gapless energy spectrum and the magnetism becomes weaker with decreasing of the $S^1$ concentration $\rho = 1/M$. While it is integer, a non-magnetic ground state with gaped spectrum emerges and the gap gradually becomes narrowed as fitted by a relation of $\Delta \approx 1.25\sqrt{\rho}$.Comment: 6 pages, 9 figure

Precise tracking of the Magellan and Pioneer Venusorbiters by same-beam interferometry. Part 1: Dataaccuracy analysis

Simultaneous tracking of two spacecraft in orbit about a distant planet by two widely separated Earth-based radio antennas provides more-accurate positioning information than can be obtained by tracking each spacecraft separately. A demonstration of this tracking technique, referred to as same-beam interferometry (SBI), is currently being done using the Magellan and Pioneer 12 orbiters at Venus. Signals from both spacecraft fall within the same beamwidth of the Deep Space Station antennas. The plane-of-sky position difference between spacecraft is precisely determined by doubly differenced phase measurements. This radio metric measurement naturally complements line-of-sight Doppler. Data was first collected from Magellan and Pioneer 12 on August 11-12, 1990, shortly after Magellan was inserted into Venus orbit. Data were subsequently acquired in February and April 1991, providing a total of 34 hours of same-beam radio metric observables. Same-beam radio metric residuals have been analyzed and compared with model measurement error predictions. The predicted error is dominated by solar plasma fluctuations. The rms of the residuals is less than predicted by about 25 percent for 5-min averages. The shape of the spectrum computed from residuals is consistent with that derived from a model of solar plasma fluctuations. This data type can greatly aid navigation of a second spacecraft when the first is well-known in its orbit

Magnetic Properties of J-J-J' Quantum Heisenberg Chains with Spin S=1/2, 1, 3/2 and 2 in a Magnetic Field

By means of the density matrix renormalization group (DMRG) method, the magnetic properties of the J-J-J$^{\prime}$ quantum Heisenberg chains with spin $S=1/2$, 1, 3/2 and 2 in the ground states are investigated in the presence of a magnetic field. Two different cases are considered: (a) when $J$ is antiferromagnetic and $J^{\prime}$ is ferromagnetic (i.e. the AF-AF-F chain), the system is a ferrimagnet. The plateaus of the magnetization are observed. It is found that the width of the plateaus decreases with increasing the ferromagnetic coupling, and disappears when $$ passes over a critical value. The saturated field is observed to be independent of the ferromagnetic coupling; (b) when $J$ is ferromagnetic and $J^{\prime}$ is antiferromagnetic (i.e. the F-F-AF chain), the system becomes an antiferromagnet. The plateaus of the magnetization are also seen. The width of the plateaus decreases with decreasing the antiferromagnetic coupling, and disappears when $J^{\prime}/J$ passes over a critical value. Though the ground state properties are quite different, the magnetization plateaus in both cases tend to disappear when the ferromagnetic coupling becomes more dominant. Besides, no fundamental difference between the systems with spin half-integer and integer has been found.Comment: 8 pages, 9 figures, to be published in J. Phys.: Condens. Matte

Translating Covid-19 information into Yiddish for the UK Hasidic community

This article documents a recent project translating COVID-19 information into Yiddish for the benefit of the Hasidic Jewish communities in London’s Stamford Hill and in Manchester in the UK. The translation work developed as a response to the urgent need for Yiddish-language resources specifically designed for the Hasidic community near the beginning of the pandemic. The translations were undertaken by a team consisting of linguists and native speakers of Hasidic Yiddish and took place within the framework of a research project funded by the UK Arts and Humanities Research Council, dedicated to linguistic and sociolinguistic analysis of contemporary Hasidic Yiddish worldwide. In this article we discuss the sociolinguistic background to the translations and investigate the reasons why they were so urgently needed, before going on to address the issues encountered during the course of the translation process and the decisions taken in order to resolve them. These issues include the type of Yiddish chosen for the translations, the translation of medical terminology, gender-based linguistic differences affecting the translations, and specific cultural considerations that needed to be taken into account

Causes de décès dans une zone rurale d'Afrique du Sud comparées à deux autres situations (Sénégal et France)

L'étude compare le profil des causes de décès dans une zone rurale de l'Afrique du Sud (Agincourt, 1992-1995) à une autre zone rurale d'Afrique de l'Ouest (Niakhar, 1983-1989) et à un pays développé ayant la même espérance de vie (la France de 1951). Cette comparaison permettra d'identifier les causes de décès ayant une fréquence particulièrement forte (ou faible) et par conséquent de dégager des priorités pour les futures actions de santé publique. Dans les deux sites africains, les causes de décès sont déterminées par autopsie verbale, alors que dans le cas de la France les données sur les causes de décès proviennent de l'enregistrement régulier par le corps médical. Dans les trois cas, les taux comparatifs de mortalité par cause ont été calculés. Sur le site d'Afrique du Sud, l'espérance de vie à la naissance était estimée à 66 ans au cours de la période 1992-1995, pratiquement identique à celle de la France de 1951, mais beaucoup plus élevée que celle de Niakhar dans les années 1983-1989 (49 ans). Les causes déterminant une mortalité particulièrement élevée à Agincourt sont les morts violentes (homicide et suicide), les accidents (accidents de la route et accidents domestiques), certaines maladies infectieuses (sida, tuberculose, diarrhée et dysenterie), et certaines maladies non-transmissibles (cancers des organes génitaux, cirrhose du foie, hémorragie gastrique, mortalité maternelle, épilepsie, rhumatisme articulaire aigu, pneumoconiose), ainsi que la malnutrition des jeunes enfants (kwashiorkor). Les causes de décès déterminant une mortalité particulièrement faible sont les maladies respiratoires (pneumonie, bronchite, grippe, cancer du poumon), les autres cancers, les maladies vaccinables (rougeole, coqueluche, tétanos) et le marasme... (D'après résumé d'auteur

Predictors of health care use by adults 50 years and over in a rural South African setting

KIMBACKGROUND: South Africa's epidemiological transition is characterised by an increasing burden of chronic communicable and non-communicable diseases. However, little is known about predictors of health care use (HCU) for the prevention and control of chronic diseases among older adults. OBJECTIVE: To describe reported health problems and determine predictors of HCU by adults aged 50+ living in a rural sub-district of South Africa. DESIGN: A cross-sectional study to measure HCU was conducted in 2010 in the Agincourt sub-district of Mpumalanga Province, an area underpinned by a robust health and demographic surveillance system. HCU, socio-demographic variables, reception of social grants, and type of medical aid were measured, and compared between responders who used health care services with those who did not. Predictors of HCU were determined by binary logistic regression adjusted for socio-demographic variables. RESULTS: Seventy-five percent of the eligible adults aged 50+ responded to the survey. Average age of the targeted 7,870 older adults was 66 years (95% CI: 65.3, 65.8), and there were more women than men (70% vs. 30%, p<0.001). All 5,795 responders reported health problems, of which 96% used health care, predominantly at public health facilities (82%). Reported health problems were: chronic non-communicable diseases (41% - e.g. hypertension), acute conditions (27% - e.g. flu and fever), other conditions (26% - e.g. musculoskeletal pain), chronic communicable diseases (3% - e.g. HIV and TB), and injuries (3%). In multivariate logistic regression, responders with chronic communicable disease (OR=5.91, 95% CI: 1.44, 24.32) and non-communicable disease (OR=2.85, 95% CI: 1.96, 4.14) had significantly higher odds of using health care compared with those with acute conditions. Responders with six or more years of education had a two-fold increased odds of using health care (OR=2.49, 95% CI: 1.27, 4.86) compared with those with no formal education. CONCLUSION: Chronic communicable and non-communicable diseases were the most prevalent and main predictors of HCU in this population, suggesting prioritisation of public health care services for chronic diseases among older people in this rural setting

Piloting an Educational Response to Violence in Uganda: Prospects for a New Curriculum

This pilot study assessed Mato-Oput5 (hereafter the curriculum), a new peace education curriculum, for indications of beneficial efficacy, specifically the capacity to reduce negative attitudes towards conflict and violence, and injury and violence rates. A cluster randomisedcontrol design was used. Three of the six purposively selected schools were exposed to the curriculum. Mato-Oput5 is a value-based, formalised curriculum taught by specifically trainedteachers. Its learning areas include conflict, conscience, violence, non-violence, impulse control, anger management, kindness, forgiveness, empathy and reconciliation. The results showed the baseline and post-intervention bio-demographic characteristics of the treatment arms to be comparable, thus suggesting baseline group equivalence and randomisation success. The follow-up loss was 9%. The mean pre- and post-intervention intentional incidentrates of the intervention and control groups were 270/1000 and 370/1000, and 190/1000 and 350/1000, respectively: these differences were not significant. The intervention had no effect onpost-intervention intentional incident rates. There were indications of beneficial efficacy in the curriculum, especially its ability to cause attitude shifts in support of non-violence. Statisticallysignificant behavioural effects were not detected although a downward rate trend was seen in the intervention group