Regenerative braking on bicycles to power LED safety flashers

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaves 28-29).This work develops a method for capturing some of the kinetic energy ordinarily lost during braking on bicycles to power LED safety flashers. The system is designed to eliminate: (a) battery changing in popular LED flashers, and (b) the "generator drag" associated with battery-less human-powered bicycle lights and flashers. System sizing, mechanical design considerations, potential end-user factors, and a model for braking frequencies in urban settings are discussed. With the urban commuter cyclist in mind as a potential user of the regenerative braking system, custom direct-pull brake calipers (or "V-Brakes") were designed and manufactured to include both conventional friction pads in addition to a DC motor to be used as a generator for kinetic energy capture. The energy captured by the DC motor during braking is passed through a full wave bridge to a bank of Nickel-Cadmium batteries at an efficiency of 79%. The output of the full wave bridge and the batteries are connected in parallel with a step-down switching voltage regulator, which insulates the LED safety flasher from voltage spikes due to braking at high cycling speeds. The performance of the final prototype was evaluated at cycling speeds ranging from 8 to 19 mph and braking frequencies ranging from 2 to 8 operations/stops per mile of travel.(cont.) From the mean power flow (charging) into the batteries per unit distance of travel and the power required by LED safety flashers, the effectiveness of the system at each speed and stopping frequency is examined. For cyclists traveling at average speeds of 10 mph or higher, the LED safety flashers can be powered continuously for stopping frequencies of 8 times per mile and semi-continuously (> 50% of the time) for stopping frequencies of at least 4 times per mile. As such, the system is determined to be potentially useful to urban commuter cyclists, who frequently perform braking operations at regularly spaced intersections and traffic signals, and who regularly travel by bicycle in low-light conditions (dawn or dusk), though usually less than 50% of the time.by Ian M. Collier.S.B

Rationing Antiretroviral Therapy for HIV/AIDS in Africa: Efficiency, Equity, and Reality

Background: Rationing of access to antiretroviral therapy already exists in sub-Saharan Africa and will intensify as national treatment programs develop. The number of people who are medically eligible for therapy will far exceed the human, infrastructural, and financial resources available, making rationing of public treatment services inevitable. Methods: We identified 15 criteria by which antiretroviral therapy could be rationed in African countries and analyzed the resulting rationing systems across 5 domains: clinical effectiveness, implementation feasibility, cost, economic efficiency, and social equity. Findings: Rationing can be explicit or implicit. Access to treatment can be explicitly targeted to priority subpopulations such as mothers of newborns, skilled workers, students, or poor people. Explicit conditions can also be set that cause differential access, such as residence in a designated geographic area, co-payment, access to testing, or a demonstrated commitment to adhere to therapy. Implicit rationing on the basis of first-come, first-served or queuing will arise when no explicit system is enforced; implicit systems almost always allow a high degree of queue-jumping by the elite. There is a direct tradeoff between economic efficiency and social equity. Interpretation: Rationing is inevitable in most countries for some period of time. Without deliberate social policy decisions, implicit rationing systems that are neither efficient nor equitable will prevail. Governments that make deliberate choices, and then explain and defend those choices to their constituencies, are more likely to achieve a socially desirable outcome from the large investments now being made than are those that allow queuing and queue-jumping to dominate

Towards the synthesis of fluoro-thromboxane A₂ analogues

Firstly, the biosynthesis and physiological role of thromboxanes and the potential for a thromboxane A₂ antagonist in cardiovascular therapy are discussed. Secondly, the importance of fluorine in drug design is outlined and the syntheses of a series of thromboxane A₂ structural analogues are reviewed. This is concluded by proposing how fluorine substitution should allow synthesis of a stable structural analogue of thromboxane A₂ which may have antagonistic properties. Finally, the synthetic conversion of a carbohydrate precursor, levoglucosan, into a suitable precursor to 10-α-flurothromboxane A₂ is discussed in detail

Wild record of an apple snail in the Waikato River, Hamilton, New Zealand and their incidence in freshwater aquaria

We report the discovery of a single specimen of a live apple snail Pomacea diffusa Blume 1957 (Ampullariidae: Prosobranchia), from the Waikato River, Hamilton city, central North Island, New Zealand. This species, along with the congeneric P. insularum, is imported for the aquarium trade, and its occurrence in the river likely stemmed from an aquarium release. A survey of 55 aquaria belonging to 43 hobbyists revealed 27 apple snails, with one owner having 22 snails. Assessment of environmental tolerances and impacts of P. diffusa, based largely on studies of the closely related and commonly confused congener P. bridgesii, suggests that direct habitat impacts by this species are likely to be minor. However, there could be indirect influences on native biodiversity through predation on eggs or competition for food supplies with other detritivorous species if densities were to become high. Water temperatures in the Waikato River below Hamilton (10-23˚C in 2009) may enable released individuals to persist for an extended period, and over summer may exceed the threshold required to enable breeding. However, population establishment would be most likely in locations where water is heated through geothermal influences or industrial cooling water discharges

The Negotiation and Development of Writing Teacher Identities in Elementary Education

Identity development in writing is a unique process. While many studies have explored the process of developing a professional identity among future teachers, few studies have investigated how teacher candidates develop a writing teacher’s identity. This study explores the development and negotiation of writing teacher identity among 21 pre-service multiple-subject teacher candidates at a large public institution in California. More specifically, the study examines the students’ journeys as they transformed from students of writing in a university methods course to student teachers of writing in a local school district. Our findings indicate that the use of a sociocultural-based approach to teaching writing in a university method’s course conflicted with the use of a skills-based mandated curriculum used in local districts. Nonetheless, within this space of conflict, teacher candidates began to determine how to merge the two approaches, understand potential limitations and develop a pedagogical toolbox thus, renegotiating their identities as future writing teachers. We provide recommendations that teacher educators may use to assist teacher candidates and developing effective writing pedagogy while utilizing a mandated curriculum

Using physical barriers to prevent carrot fly (Psila rosae (Fabricius)) damage in domestic production

A field experiment was used to assess the effectiveness of different barriers in protecting garden‐scale carrot production from carrot fly (Psila rosae (Fabricius)) damage. Some of the vertical barriers tested were found to provide a useful method of protecting early season carrots from carrot fly in terms of the percentage of carrots free from damage but, under cumulative pest pressure of several generations of carrot fly, such barriers were found to provide insufficient protection. Gardeners should therefore completely cover their carrot crop to attain an acceptable level of control, and this was found to be especially important for carrots harvested later in the season. There were positive effects of some barrier types on yield which may be due, at least in part, to the protection given by the barriers to carrot seedlings

Correlating AFM Probe Morphology to Image Resolution for Single-Wall Carbon Nanotube Tips

We report local-field-enhanced light emission from silicon nanocrystals close to a film of nanoporous gold. We resolve photoluminescence as the gold−Si nanocrystal separation distance is varied between 0 and 20 nm and observe a fourfold luminescence intensity enhancement concomitant with increases in the coupled silicon nanocrystal/nanoporous gold absorbance cross section and radiative decay rate. A detailed analysis of the luminescence data indicated a local-field-enhanced quantum efficiency of 58% for the Si nanocrystals coupled to the nanoporous gold layer

Guidelines for Secure Operation of Attribute Authorities and issuers of statements for entities (G071)

These guidelines describe the minimum requirements and recommendations for the secure operation of attribute authorities and similar services that make statements about an entity based on well-defined attributes. Adherence to these guidelines may help to establish trust between communities, operators of attribute authorities and issuers, and Relying Parties, infrastructures, and service providers. This document does not define an accreditation process

TGF-β isoforms fail to modulate inositol phosphates and cAMP in normal and tumour-derived human oral keratinocytes

AbstractThis study examined inositol phosphate and cAMP regulation by TGF-β1, -β2 and -β3 in normal and tumour-derived human oral keratinocytes. Previous findings indicated that the cell lines expressed TGF-β cell surface receptors and had a range of response to exogenous TGF-β1, -β2 and -β3 from being refractory to the ligand to marked inhibition. Basal levels of inositol phosphates broadly reflected the differentiation status of the cells as demonstrated by involucrin expression, but did not correlate with responsiveness to TGF-β1, as measured previously by thymidine incorporation. Treatment of cells with bradykinin or serum caused up-regulation of inositol phosphate levels; by contrast, TGF-β1, -β2 and -β3 failed to modulate inositol phosphates. In two tumour-derived cell lines, the TGF-β isoforms had no effect on cAMP levels, despite a significant increase in cAMP using a potent agonist of adenylate cyclase (forskolin). Furthermore, the cAMP analogue, dibutyryl cAMP, failed to mimic the inhibitory or refractory responses of TGF-β in these cell lines. The results demonstrate that in normal and tumour-derived human oral keratinocytes, TGF-β signal transduction is not mediated by inositol phosphates or cAMP