P-matrices and signed digraphs

We associate a signed digraph with a list of matrices whose dimensions permit them to be multiplied, and whose product is square. Cycles in this graph have a parity, that is, they are either even (termed e-cycles) or odd (termed o-cycles). The absence of e-cycles in the graph is shown to imply that the matrix product is a P0-matrix, i.e., all of its principal minors are nonnegative. Conversely, the presence of an e-cycle is shown to imply that there exists a list of matrices associated with the graph whose product fails to be a P0-matrix. The results generalise a number of previous results relating P- and P0-matrices to graphs

Behaviour of dairy cows on organic and non-organic farms

There is an increasing number of organic dairy farms in the UK. The aim of this study is to compare behaviour of dairy cows on organic and non-organic farms. Twenty organic and 20 non-organic farms throughout the UK were visited over two winters (2004/05 and 2005/06). Organic and non-organic farms were paired for housing type, herd size, milk production traits and location. The number of cows feeding was counted every fifteen minutes for 4.5 h after new feed was available post morning milking. Behaviour at the feed-face was recorded for 60 minutes and aggressive interactions between cows were quantified. Farm type had no effect on numbers of cows feeding. There were more interactions between cows feeding at open feed-faces compared to head-bale barriers. At open feed-faces, there were more interactions on organic farms than non-organic. It is possible that organic cows were hungrier than non-organic cows after the arrival of new feed

The evolution of morality

Morality is essential to human identity. Since Darwin and Wallace proposed natural selection to explain the complexities of organisms, evolutionary biologists have sought explanations for all aspects of human nature including morality. One way to establish how far morality is to humans is to examine moral precursors in closely-related species. The advantage of such a characteristic initially seems contrary to the 'selfish' process of natural selection, however various ways in which such a trait has adaptive value have been proposed. Also the extent to which morality is actually part of human identity, a product of sophisticated human culture rather than being hard-wired into our minds by evolutionary process, is a fascinating and current area of scientific dialogue

Some results on the structure and spectra of matrix-products

We consider certain matrix-products where successive matrices in the product belong alternately to a particular qualitative class or its transpose. The main theorems relate structural and spectral properties of these matrix-products to the structure of underlying bipartite graphs. One consequence is a characterisation of caterpillars: a graph is a caterpillar if and only if all matrix-products associated with it have real nonnegative spectrum. Several other equivalences of this kind are proved. The work is inspired by certain questions in dynamical systems where such products arise naturally as Jacobian matrices, and the results have implications for the existence and stability of equilibria in these systems

Effects of a falls exercise intervention on strength, power, functional ability and bone in older frequent fallers: FaME (Falls Management Exercise) RCT secondary analysis

OBJECTIVES: Falls Management Exercise (FaME) has been shown to reduce falls in frequent fallers and in lower risk sedentary older people. The effects of FaME on the strength, power, physical function and bone health of frequently falling older women are yet to be established. METHODS: This paper reports secondary analysis of data from the original randomised controlled trial of FaME in 100 community dwelling women aged ≥65 years with a history of ≥3 falls in the previous year. Intervention was group delivered, weekly one hour tailored dynamic balance and strength exercise classes and home exercise for nine months. OUTCOME MEASURES INCLUDED: strength (handgrip, quadriceps, hamstrings, hip abductors, ankles), lower limb explosive power and functional tests (timed up and go, functional reach, timed floor rise and balance), analysed using Linear Mixed Model analysis. Bone Mineral Density (BMD) at hip and spine was measured in a smaller sub-group and analysed using t-tests. RESULTS: Significant time*group interactions in all measures of strength, except isometric ankle dorsiflexion, concentric hamstring and eccentric quadriceps strength. These improvements in strength equated to average improvements of 7-45%. There were also significant improvements in explosive power (W/kg) (18%, p=0.000), timed up and go (16%, p=0.000), functional reach (17%, p=0.000), floor rise (10%, p=0.002) and eyes closed static balance (56%, p=0.000). There was a significant loss of hip BMD in the control group (neck of femur p<0.05; ward's triangle p<0.02). CONCLUSION: The FaME intervention improves lower limb strength, power and clinically relevant functional outcomes in frequently falling older women

Reexamining the Impact of Employee Relocation Assistance on Housing Prices

In this paper, we reexamine the issue of whether corporate relocation assistance programs for transferred employees significantly affect sale prices of single-family homes. We estimate a hedonic price equation that includes physical housing characteristics, location factors, occupancy status, and type of seller for a sample of 2,441 transactions. Seller types include (a) transferred employees who were given direct relocation assistance, (b) transferred employees who were not given direct relocation assistance, and (c) sellers who were not facing an employment transfer. After controlling for vacancy and tenant occupancy, we find that houses sold by transferred employees who receive direct relocation assistance exhibit no significant price differential, but that houses sold by transferred employees who do not receive direct relocation assistance sell at a discount of approximately 3%.

Screening for Park Access during a Primary Care Social Determinants Screen.

While there is evidence that access to nature and parks benefits pediatric health, it is unclear how low-income families living in an urban center acknowledge or prioritize access to parks.MethodsWe conducted a study about access to parks by pediatric patients in a health system serving low-income families. Adult caregivers of pediatric patients completed a survey to identify and prioritize unmet social and economic needs, including access to parks. Univariate and multivariate analyses were conducted to explore associations between lack of access to parks and sociodemographic variables. We also explored the extent to which access to parks competed with other needs.ResultsThe survey was completed by 890 caregivers; 151 (17%) identified "access to green spaces/parks/playgrounds" as an unmet need, compared to 397 (45%) who endorsed "running out of food before you had money or food stamps to buy more". Being at or below the poverty line doubled the odds ( Odds ratio 1.96, 95% CI 1.16-3.31) of lacking access to a park (reference group: above the poverty line), and lacking a high school degree nearly doubled the odds. Thirty-three of the 151 (22%) caregivers who identified access to parks as an unmet need prioritized it as one of three top unmet needs. Families who faced competing needs of housing, food, and employment insecurity were less likely to prioritize park access (p < 0.001).ConclusionClinical interventions to increase park access would benefit from an understanding of the social and economic adversity faced by patients