Dalhousie University

About: Dalhousie University is a education organization based out in Halifax, Nova Scotia, Canada. It is known for research contribution in the topics: Population & Health care. The organization has 25660 authors who have published 58465 publications receiving 2082403 citations. The organization is also known as: Dalhousie College & The Governors of Dalhousie College and University.

Thickness and Elasticity of Gram-Negative Murein Sacculi Measured by Atomic Force Microscopy

Abstract: Atomic force microscopy was used to measure the thickness of air-dried, collapsed murein sacculi from Escherichia coli K-12 and Pseudomonas aeruginosa PAO1. Air-dried sacculi from E. coli had a thickness of 3.0 nm, whereas those from P. aeruginosa were 1.5 nm thick. When rehydrated, the sacculi of both bacteria swelled to double their anhydrous thickness. Computer simulation of a section of a model single-layer peptidoglycan network in an aqueous solution with a Debye shielding length of 0.3 nm gave a mass distribution full width at half height of 2.4 nm, in essential agreement with these results. When E. coli sacculi were suspended over a narrow groove that had been etched into a silicon surface and the tip of the atomic force microscope used to depress and stretch the peptidoglycan, an elastic modulus of 2.5 x 10(7) N/m(2) was determined for hydrated sacculi; they were perfectly elastic, springing back to their original position when the tip was removed. Dried sacculi were more rigid with a modulus of 3 x 10(8) to 4 x 10(8) N/m(2) and at times could be broken by the atomic force microscope tip. Sacculi aligned over the groove with their long axis at right angles to the channel axis were more deformable than those with their long axis parallel to the groove axis, as would be expected if the peptidoglycan strands in the sacculus were oriented at right angles to the long cell axis of this gram-negative rod. Polar caps were not found to be more rigid structures but collapsed to the same thickness as the cylindrical portions of the sacculi. The elasticity of intact E. coli sacculi is such that, if the peptidoglycan strands are aligned in unison, the interstrand spacing should increase by 12% with every 1 atm increase in (turgor) pressure. Assuming an unstressed hydrated interstrand spacing of 1.3 nm (R. E. Burge, A. G. Fowler, and D. A. Reaveley, J. Mol. Biol. 117:927-953, 1977) and an internal turgor pressure of 3 to 5 atm (or 304 to 507 kPa) (A. L. Koch, Adv. Microbial Physiol. 24:301-366, 1983), the natural interstrand spacing in cells would be 1.6 to 2.0 nm. Clearly, if large macromolecules of a diameter greater than these spacings are secreted through this layer, the local ordering of the peptidoglycan must somehow be disrupted.

What would make a definition of frailty successful

Abstract: At present, frailty is defined variably. Some consensus on a definition is likely to emerge, but the basis for a successful definition needs to be explored. Here, a classic approach to validation is proposed: a successful definition of frailty should be multifactorial but must also manage the many factors in a way that takes their interactions into account. It is likely to be correlated with disability, co-morbidity and self-rated health, and should identify a group that is vulnerable to adverse outcomes. Ideally, it should also be susceptible to animal modelling. In that frailty and age are so bound together, it is also likely that there will be some age at which virtually all people will be frail, by any definition. Apart from being valid, the success of any definition of frailty will depend on it being useful to researchers and clinicians. The need for progress on our understanding of frailty is evident, but for now, there is insufficient evidence to accept a single definition of frailty.

Evaluating claims-based indicators of the intensity of end-of-life cancer care

Abstract: Objective. To evaluate measures that could use existing administrative data to assess the intensity of end-of-life cancer care. Methods. Benchmarking standards and statistical variation were evaluated using Medicare claims of 48,906 patients who died from cancer from 1991 through 1996 in 11 regions of the United States. We assessed accuracy by comparing administrative data to 150 medical records in one hospital and affiliated cancer treatment center. Results. Systems not providing overly aggressive care near the end of life would be ones in which less than 10% of patients receive chemotherapy in the last 14 days of life, less than 2% start a new chemotherapy regimen in the last 30 days of life, less than 4% have multiple hospitalizations or emergency room visits or are admitted to the intensive care unit (ICU) in the last month of life, and less than 17% die in an acute care institution. At least 55% of patients would receive hospice services before death from cancer, and less than 8% of those would be admitted to hospice within only 3 days of death. All measures were found to have accuracy ranging from 85 to 97% and 2- to 5-fold adjusted variability between the 5th and 95th percentiles of performance. Conclusions. The usefulness of these measures will depend on whether the concept of intensity of care near death can be further validated as an acceptable and important quality issue among patients, their families, health care providers, and other stakeholders in oncology.

The biology of Pseudocalanus.

Abstract: Publisher Summary Pseudocalanus is typical of most crustaceans in that after hatching at an early stage of development it adds successively new segments and appendages. Pseudocalanus hatches as a nauplius, which is the most immature larval form among the arthropods. Respiration of Pseudocalanus has been quite extensively documented, generally as one of a number of forms in comparative studies. Respiration is measured as oxygen consumption. Even if morphological differences among geographically isolated populations of Pseudocalanus are elusive, physiological differences occur that may signify reproductive isolation. In recent years, a novel source of variations within and between populations of Pseudocalanus has been discovered. McLaren described a large form of Pseudocalanus that coexists with a more abundant small form in Ogac Lake, a partially landlocked fiord on Baffin Island, northern Canada. The small form was believed to be the same as the widespread Pseudoealanus of waters outside the fiord, the size of which had been reduced inside the fiord by elevated temperatures. In considering the limits of the range of Pseudocalanus, Sewell cites records from as far south as Chesapeake Bay in the eastern U.S.A., from the North Atlantic Drift south of Iceland, from European waters as far south as Portugal, and from the Mediterranean. In the North Pacific, he records it south to Japan and Vancouver Island.

IoT Goes Nuclear: Creating a ZigBee Chain Reaction

Abstract: Within the next few years, billions of IoT devices will densely populate our cities. In this paper we describe a new type of threat in which adjacent IoT devices will infect each other with a worm that will rapidly spread over large areas, provided that the density of compatible IoT devices exceeds a certain critical mass. In particular, we developed and verified such an infection using the popular Philips Hue smart lamps as a platform. The worm spreads by jumping directly from one lamp to its neighbors, using only their built-in ZigBee wireless connectivity and their physical proximity. The attack can start by plugging in a single infected bulb anywhere in the city, and then catastrophically spread everywhere within minutes. It enables the attacker to turn all the city lights on or off, to permanently brick them, or to exploit them in a massive DDOS attack. To demonstrate the risks involved, we use results from percolation theory to estimate the critical mass of installed devices for a typical city such as Paris whose area is about 105 square kilometers: The chain reaction will fizzle if there are fewer than about 15,000 randomly located smart lamps in the whole city, but will spread everywhere when the number exceeds this critical mass (which had almost certainly been surpassed already). To make such an attack possible, we had to find a way to remotely yank already installed lamps from their current networks, and to perform over-the-air firmware updates. We overcame the first problem by discovering and exploiting a major bug in the implementation of the Touchlink part of the ZigBee Light Link protocol, which is supposed to stop such attempts with a proximity test. To solve the second problem, we developed a new version of a side channel attack to extract the global AES-CCM key (for each device type) that Philips uses to encrypt and authenticate new firmware. We used only readily available equipment costing a few hundred dollars, and managed to find this key without seeing any actual updates. This demonstrates once again how difficult it is to get security right even for a large company that uses standard cryptographic techniques to protect a major product.