How to play a disc brake

We consider a gyroscopic system under the action of small dissipative and non-conservative positional forces, which has its origin in the models of rotating bodies of revolution being in frictional contact. The spectrum of the unperturbed gyroscopic system forms a "spectral mesh" in the plane "frequency -gyroscopic parameter" with double semi-simple purely imaginary eigenvalues at zero value of the gyroscopic parameter. It is shown that dissipative forces lead to the splitting of the semi-simple eigenvalue with the creation of the so-called "bubble of instability" - a ring in the three-dimensional space of the gyroscopic parameter and real and imaginary parts of eigenvalues, which corresponds to complex eigenvalues. In case of full dissipation with a positive-definite damping matrix the eigenvalues of the ring have negative real parts making the bubble a latent source of instability because it can "emerge" to the region of eigenvalues with positive real parts due to action of both indefinite damping and non-conservative positional forces. In the paper, the instability mechanism is analytically described with the use of the perturbation theory of multiple eigenvalues. As an example stability of a rotating circular string constrained by a stationary load system is studied in detail. The theory developed seems to give a first clear explanation of the mechanism of self-excited vibrations in the rotating structures in frictional contact, that is responsible for such well-known phenomena of acoustics of friction as the squealing disc brake and the singing wine glass.Comment: 25 pages, 9 figures, Presented at BIRS 07w5068 Workshop "Geometric Mechanics: Continuous and discrete, finite and infinite dimensional", August 12-17, 2007, Banff, Canad

The directional contact distance of two ellipsoids: Coarse-grained potentials for anisotropic interactions

Copyright @ 2005 American Institute of Physics.We obtain the distance of closest approach of the surfaces of two arbitrary ellipsoids valid at any orientation and separation measured along their intercenter vector. This directional distance is derived from the elliptic contact function. The geometric meaning behind this approach is clarified. An elliptic pair potential for modeling arbitrary mixtures of elliptic particles, whether hard or soft, is proposed based on this distance. Comparisons with Gay-Berne potentials are discussed. Analytic expressions for the forces and torques acting on the elliptic particles are given.This research has been supported by GlaxoSmith-Klin

Is the Web ready for HTTP/2 Server Push?

HTTP/2 supersedes HTTP/1.1 to tackle the performance challenges of the modern Web. A highly anticipated feature is Server Push, enabling servers to send data without explicit client requests, thus potentially saving time. Although guidelines on how to use Server Push emerged, measurements have shown that it can easily be used in a suboptimal way and hurt instead of improving performance. We thus tackle the question if the current Web can make better use of Server Push. First, we enable real-world websites to be replayed in a testbed to study the effects of different Server Push strategies. Using this, we next revisit proposed guidelines to grasp their performance impact. Finally, based on our results, we propose a novel strategy using an alternative server scheduler that enables to interleave resources. This improves the visual progress for some websites, with minor modifications to the deployment. Still, our results highlight the limits of Server Push: a deep understanding of web engineering is required to make optimal use of it, and not every site will benefit.Comment: More information available at https://push.netray.i

Great cities look small

Great cities connect people; failed cities isolate people. Despite the fundamental importance of physical, face-to-face social-ties in the functioning of cities, these connectivity networks are not explicitly observed in their entirety. Attempts at estimating them often rely on unrealistic over-simplifications such as the assumption of spatial homogeneity. Here we propose a mathematical model of human interactions in terms of a local strategy of maximising the number of beneficial connections attainable under the constraint of limited individual travelling-time budgets. By incorporating census and openly-available online multi-modal transport data, we are able to characterise the connectivity of geometrically and topologically complex cities. Beyond providing a candidate measure of greatness, this model allows one to quantify and assess the impact of transport developments, population growth, and other infrastructure and demographic changes on a city. Supported by validations of GDP and HIV infection rates across United States metropolitan areas, we illustrate the effect of changes in local and city-wide connectivities by considering the economic impact of two contemporary inter- and intra-city transport developments in the United Kingdom: High Speed Rail 2 and London Crossrail. This derivation of the model suggests that the scaling of different urban indicators with population size has an explicitly mechanistic origin.Comment: 19 pages, 8 figure

Metformin induces distinct bioenergetic and metabolic profiles in sensitive versus resistant high grade serous ovarian cancer and normal fallopian tube secretory epithelial cells.

Metformin is a widely used agent for the treatment of diabetes and infertility, however, it has been found to have anti-cancer effects in a variety of malignancies including high grade serous ovarian cancer (HGSC). Studies describing the mechanisms by which metformin affects HGSC are ongoing, but detailed analysis of its effect on the cellular metabolism of both HGSC cells and their precursor, normal fallopian tube secretory epithelial cells (FTSECs), is lacking. We addressed the effects of metformin and the more potent biguanide, phenformin, on HGSC cell lines and normal immortalized FTSECs. Cell proliferation assays identified that FTSECs and a subset of HGSC cell lines are relatively resistant to the anti-proliferative effects of metformin. Bioenergetic and metabolomic analyses were used to metabolically differentiate the metformin-sensitive and metformin-resistant cell lines. Bioenergetically, biguanides elicited a significant decrease in mitochondrial respiration in all HGSC cells and FTSECs. However, biguanides had a greater effect on mitochondrial respiration in metformin sensitive cells. Metabolomic analysis revealed that metformin and phenformin generally induce similar changes in metabolic profiles. Biguanide treatment led to a significant increase in NADH in FTSECs and HGSC cells. Interestingly, biguanide treatment induced changes in the levels of mitochondrial shuttle metabolites, glycerol-3-phopshate (G3P) and aspartate, specifically in HGSC cell lines and not in FTSECs. Greater alterations in G3P or aspartate levels were also found in metformin sensitive cells relative to metformin resistant cells. These data identify bioenergetic and HGSC-specific metabolic effects that correlate with metformin sensitivity and novel metabolic avenues for possible therapeutic intervention

Utility of 2013 American College of Cardiology/American Heart Association Cholesterol Guidelines in HIV-Infected Adults With Carotid Atherosclerosis.

BackgroundAlthough HIV is associated with increased atherosclerotic cardiovascular disease (CVD) risk, it is unknown whether guidelines can identify HIV-infected adults who may benefit from statins. We compared the 2013 American College of Cardiology/American Heart Association and 2004 Adult Treatment Panel III recommendations in HIV-infected adults and evaluated associations with carotid artery intima-media thickness and plaque.Methods and resultsCarotid artery intima-media thickness was measured at baseline and 3 years later in 352 HIV-infected adults without clinical atherosclerotic CVD and not on statins. Plaque was defined as IMT >1.5 mm in any segment. At baseline, the median age was 43 (interquartile range, 39-49), 85% were men, 74% were on antiretroviral medication, and 50% had plaque. The American College of Cardiology/American Heart Association guidelines were more likely to recommend statins compared with the Adult Treatment Panel III guidelines, both overall (26% versus 14%; P<0.001), in those with plaque (32% versus 17%; P=0.0002), and in those without plaque (16% versus 7%; P=0.025). In multivariable analysis, older age, higher low-density lipoprotein cholesterol, pack per year of smoking, and history of opportunistic infection were associated with baseline plaque. Baseline IMT (hazard ratio, 1.18 per 10% increment; 95% confidence interval, 1.05-1.33; P=0.005) and plaque (hazard ratio, 2.06; 95% confidence interval, 1.02-4.08; P=0.037) were each associated with all-cause mortality, independent of traditional CVD risk factors.ConclusionsAlthough the American College of Cardiology/American Heart Association guidelines recommended statins to a greater number of HIV-infected adults compared with the Adult Treatment Panel III guidelines, both failed to recommend therapy in the majority of HIV-affected adults with carotid plaque. Baseline carotid atherosclerosis but not atherosclerotic CVD risk scores was an independent predictor of mortality. HIV-specific guidelines that include detection of subclinical atherosclerosis may help to identify HIV-infected adults who are at increased atherosclerotic CVD risk and may be considered for statins

Wishes and Grumbles

This report summarises the 'wishes and grumbles' session from the Ninth UK Stata Users Group meeting.

Reality Orientation Program in RLA Stage 4 Traumatic Brain Injury Patients

AIM : To find the effectiveness of Reality Orientation Program for RLA stage 4 traumatic brain injury patients. METHODS : 20 patients were recruited for the study. Of which 10 patients underwent Reality Orientation Program (ROP) and 10 underwent Conventional therapy. The patients were administered with Galveston Amnesia and Orientation Test (GOAT), Mini Mental Status Examination (MMSE), Rancho Los Amigos Scale (RLA), Glasgow Coma Scale (GCS) and Glasgow Outcome Score (GOS). The study period was for 4 weeks, two weeks given by the therapist and family members (under the supervision of therapist) in the hospital and remaining two weeks orientation was provided by the family members either in home or hospital. RESULTS : The duration of Post Traumatic Amnesia (PTA) was reduced by 10 days for the patients who received ROP. Even though the results were not statistically significant perhaps were clinically relevant (p= 0.096). Correlation between age & GCS (r=.234), age & PTA (r=.242) and GCS & PTA (r=.050) showed no positive correlation. On comparison of the MMSE scores between groups it exhibited statistical significance at the end of fourth week. Other scales did not display statistical significance. On comparison of scales within the group it revealed high statistical significance. On comparing the significance of effectiveness it was found that MMSE scores had medium effect (ηp2=.070), GCS had very low effect ηp2=.000, small effect size (ηp2=.049) for RLA, and GOAT revealed medium effect (ηp2=.087) between group. Resolution of time, place and person in experimental group had a mean of 30, 22 and 14 days respectively whereas in control group the mean was 38, 23 and 17 days. CONCLUSION : Length of PTA was shorter in the patients who received ROP. ROP included the orientation board which reduced the confusion of the therapist and burden on the family members and enabled them to participate more actively in the treatment