Solving frustration-free spin systems

We identify a large class of quantum many-body systems that can be solved exactly: natural frustration-free spin-1/2 nearest-neighbor Hamiltonians on arbitrary lattices. We show that the entire ground state manifold of such models can be found exactly by a tensor network of isometries acting on a space locally isomorphic to the symmetric subspace. Thus, for this wide class of models real-space renormalization can be made exact. Our findings also imply that every such frustration-free spin model satisfies an area law for the entanglement entropy of the ground state, establishing a novel large class of models for which an area law is known. Finally, we show that our approach gives rise to an ansatz class useful for the simulation of almost frustration-free models in a simple fashion, outperforming mean field theory.Comment: 5 pages, 1 figur

A Qualitative Study on Female Resident Assistants & Perceived Stress

Researchers have shown female college students tend to experience stress more often than their male counterparts. However, there is little research regarding female resident assistants and their experiences with stress. In this qualitative study I focused on how female resident assistants perceive stress in their lives. The study was conducted at a small, private, evangelical institution in the Midwest and was guided by four research questions relating to how stress unique to this student leadership role impacts overall student success and well-being. In this study I found female resident assistants do experience stress in a variety of ways, both related and unrelated to being a resident assistant, but are generally able to balance their leadership role with all other areas of their lives

Gamma-Ray Bursts observed by XMM-Newton

Analysis of observations with XMM-Newton have made a significant contribution to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area, bandpass and resolution of the EPIC instrument permit the study of a wide variety of spectral features. In particular, strong, time-dependent, soft X-ray emission lines have been discovered in some bursts. The emission mechanism and energy source for these lines pose major problems for the current generation of GRB models. Other GRBs have intrinsic absorption, possibly related to the environment around the progenitor, or possible iron emission lines similar to those seen in GRBs observed with BeppoSAX. Further XMM-Newton observations of GRBs discovered by the Swift satellite should help unlock the origin of the GRB phenomenon over the next few years.Comment: To appear in proceedings of the "XMM-Newton EPIC Consortium meeting, Palermo, 2003 October 14-16", published in Memorie della Societa Astronomica Italian

Towards Real-Time Information Processing of Sensor Network Data using Computationally Efficient Multi-output Gaussian Processes

In this paper, we describe a novel, computationally efficient algorithm that facilitates the autonomous acquisition of readings from sensor networks (deciding when and which sensor to acquire readings from at any time), and which can, with minimal domain knowledge, perform a range of information processing tasks including modelling the accuracy of the sensor readings, predicting the value of missing sensor readings, and predicting how the monitored environmental variables will evolve into the future. Our motivating scenario is the need to provide situational awareness support to first responders at the scene of a large scale incident, and to this end, we describe a novel iterative formulation of a multi-output Gaussian process that can build and exploit a probabilistic model of the environmental variables being measured (including the correlations and delays that exist between them). We validate our approach using data collected from a network of weather sensors located on the south coast of England

Information Agents for Pervasive Sensor Networks

In this paper, we describe an information agent, that resides on a mobile computer or personal digital assistant (PDA), that can autonomously acquire sensor readings from pervasive sensor networks (deciding when and which sensor to acquire readings from at any time). Moreover, it can perform a range of information processing tasks including modelling the accuracy of the sensor readings, predicting the value of missing sensor readings, and predicting how the monitored environmental parameters will evolve into the future. Our motivating scenario is the need to provide situational awareness support to first responders at the scene of a large scale incident, and we describe how we use an iterative formulation of a multi-output Gaussian process to build a probabilistic model of the environmental parameters being measured by local sensors, and the correlations and delays that exist between them. We validate our approach using data collected from a network of weather sensors located on the south coast of England

A Gaussian process framework for modelling instrumental systematics: application to transmission spectroscopy

Transmission spectroscopy, which consists of measuring the wavelength-dependent absorption of starlight by a planet's atmosphere during a transit, is a powerful probe of atmospheric composition. However, the expected signal is typically orders of magnitude smaller than instrumental systematics, and the results are crucially dependent on the treatment of the latter. In this paper, we propose a new method to infer transit parameters in the presence of systematic noise using Gaussian processes, a technique widely used in the machine learning community for Bayesian regression and classification problems. Our method makes use of auxiliary information about the state of the instrument, but does so in a non-parametric manner, without imposing a specific dependence of the systematics on the instrumental parameters, and naturally allows for the correlated nature of the noise. We give an example application of the method to archival NICMOS transmission spectroscopy of the hot Jupiter HD 189733, which goes some way towards reconciling the controversy surrounding this dataset in the literature. Finally, we provide an appendix giving a general introduction to Gaussian processes for regression, in order to encourage their application to a wider range of problems.Comment: 6 figures, 1 table, accepted for publication in MNRA

Achievable Qubit Rates for Quantum Information Wires

Suppose Alice and Bob have access to two separated regions, respectively, of a system of electrons moving in the presence of a regular one-dimensional lattice of binding atoms. We consider the problem of communicating as much quantum information, as measured by the qubit rate, through this quantum information wire as possible. We describe a protocol whereby Alice and Bob can achieve a qubit rate for these systems which is proportional to N^(-1/3) qubits per unit time, where N is the number of lattice sites. Our protocol also functions equally in the presence of interactions modelled via the t-J and Hubbard models

Partnership Instability and Child Wellbeing during the Transition to Elementary School

Data from the Fragile Families and Child Wellbeing Study (N = 2,957) are used to examine partnership instability and children’s wellbeing during the transition to elementary school. We find that coresidential transitions are related to externalizing, attention, and social problems. Mothers’ mental health and use of harsh parenting partially mediate the associations between coresidential transitions and child outcomes at age five. The impact of coresidential transitions on externalizing, attention, and social problems is stronger for boys than girls. Also, non-coresidential transitions predict externalizing and attention problems for White children but not for Hispanic children. Finally, the association between coresidential transitions and verbal ability is stronger for children with highly educated mothers than for children of less educated mothers.

Meaningful CSR Communication via Digital Media

It has regularly been stated that consumer demand for CSR is larger than ever, but do consumers really want to be informed about the ethical behaviour of brands? Does digital media have an impact on meaningful CSR communication? A research analysing consumer reaction to social media posts about CSR is limited. Using mixed method, this study examined the UK consumer attitudes towards CSR and its communication in digital media plus its consequent effect on purchasing intentions. Results indicate that consumers are more likely to evaluate a brand higher if made aware of CSR activity, which in turn affects purchase intention. Consumers have fairly positive attitudes about CSR communicated on digital media, but may react negatively if the message contradicts prior behaviour of the brand. Overall, the study show support for the communication of digital media but brands looking to enhance a damaged reputation must take great consideration over the message at hand

Integrating data to facilitate clinical research : a case study

The integration of routine clinical administrative activities into ongoing rigorous clinical research poses challenges for both clinicians and researchers. This case study describes the development of a responsive database system used to facilitate comprehensive longitudinal research into the outcomes of patients waiting for hip and knee replacement surgery in a large public teaching hospital. The initial research procedure was paper-based, with manual patient matching and data entry. This process was time-consuming and associated with substantial risk of error and omissions, necessitating the design of a better system. An integrated database system was designed to receive daily electronic updates of the orthopaedic waiting-list and scheduled clinic and surgery dates. Using readily available software (Microsoft Access), new patients were identified through specifying inclusion and exclusion criteria which allowed rapid and complete recruitment at time of entry to the waiting-list. The integrated system specified the appropriate timing of multiple follow-up assessments, provided prompt information on recruitment for reporting purposes and integrated multiple linked research projects within one database. Seamless exporting of data to statistical programs for analysis was also enabled. This simple integrated approach facilitated efficient execution of a longitudinal study from recruitment to statistical analysis while maximising confidentiality and minimising resources required. This case study describes the development and design of a simple system which could be easily adapted for database management in hospital or clinic-based settings according to local requirements.<br /