Random walks with thermalizing collisions in bounded regions; physical applications valid from the ballistic to diffusive regimes

The behavior of a spin undergoing Larmor precession in the presence of fluctuating fields is of interest to workers in many fields. The fluctuating fields cause frequency shifts and relaxation which are related to their power spectrum, which can be determined by taking the Fourier transform of the auto-correlation functions of the field fluctuations. Recently we have shown how to calculate these correlation functions for all values of mean free path (ballistic to diffusive motion) in finite bounded regions, using the model of persistent continuous time random walks (CTRW) for particles subject to scattering by fixed (frozen) scattering centers so that the speed of the moving particles is not changed by the collisions. In this work we show how scattering with energy exchange from an ensemble of scatterers in thermal equilibrium can be incorporated into the CTRW. We present results for 1,2 and 3 dimensions. The results agree for all these cases contrary to the previously studied 'frozen' models. Our results for the velocity autocorrelation function show a long time tail $\left( \sim t^{-1/2}\right)$, which we also obtain from conventional diffusion theory, with the same power, independent of dimensionality. Our results are valid for any Markovian scattering kernel as well as any kernel based on a scattering cross section $\sim1/v.$Comment: 43 pages, 12 figure

A Generative Model for Parts-based Object Segmentation

The Shape Boltzmann Machine (SBM) [1] has recently been introduced as a stateof-the-art model of foreground/background object shape. We extend the SBM to account for the foreground object’s parts. Our new model, the Multinomial SBM (MSBM), can capture both local and global statistics of part shapes accurately. We combine the MSBM with an appearance model to form a fully generative model of images of objects. Parts-based object segmentations are obtained simply by performing probabilistic inference in the model. We apply the model to two challenging datasets which exhibit significant shape and appearance variability, and find that it obtains results that are comparable to the state-of-the-art. There has been significant focus in computer vision on object recognition and detection e.g. [2], but a strong desire remains to obtain richer descriptions of objects than just their bounding boxes. One such description is a parts-based object segmentation, in which an image is partitioned into multiple sets of pixels, each belonging to either a part of the object of interest, or its background. The significance of parts in computer vision has been recognized since the earliest days of th

Tribological properties of ceramic/Ti3Al-Nb sliding couples for use as candidate seal materials to 700 deg C

Tribological properties of Ti3Al-Nb intermetallic disks sliding against alumina-boria-silicate fabric were ascertained in air at temperatures from 25 to 700 C. These materials are candidates for sliding seal applications for the National AeroSpace Plane. The tests were done using a pin on disk tribometer. Sliding was unidirectional at 0.27 m/sec under a nominal contact stress of 340 kPa. Gold sputter or ion plating deposited films were used to reduce friction and wear. Rhodium and palladium films were used beneath the gold lubricating films to prevent diffusion of the substrate into the gold at high temperature. The friction and wear of the unlubricated specimens was unacceptable. Friction coefficients were generally greater than 1.0. The ion plated gold films, when used with a rhodium diffusion barrier reduced friction by almost a factor of 2. Wear was also substantially reduced. The sputter deposited films were not adherent unless the substrate was sputter cleaned immediately prior to film deposition. Palladium did not function as a diffusion barrier

Marketing Ecosystem Services from Agricultural Land: Stated Preferences over Payment Mechanisms and Actual Sales of Farm-Wildlife Contracts

Agriculture conventionally supplies food, fiber and fuel that consumers can purchase through the market. With the right incentives, farmers can also provide ecosystem services such as wildlife habitat, climate regulation, surface water flows and waste absorption and breakdown. Such incentives have so far come almost entirely from government-sponsored programs that rely on financial assistance to farmers to encourage them to alter agricultural practices or input mix to enhance ecosystem services. Programs recently implemented in Costa Rica and Columbia rely on payments by the beneficiaries of the ecosystem services, such as municipal water companies and water users (Pagiola et al. 2002). Few of these programs, however, have attempted to establish a market for ecosystem services in which the beneficiaries of such services pay the suppliers their personal values of ecosystem services in an actual market. Markets for ecosystem services must overcome two major challenges. In order to set prices for ecosystem services at the right level, it is imperative to understand consumers preferences. Farmland, however, has multiple attributes such as wildlife habitat services and landscape view; the marginal rate of substitution among those attributes must be understood to design marketable products for ecosystem services. Moreover, many ecosystem services are public goods for which traditional markets are ill-suited, because many individuals can receive benefits simultaneously regardless of whether they have paid part of the cost of provision. Therefore, consumers have an incentive to free-ride on others. Evidence from previous research on public goods clearly suggests that under-contribution is typical (e.g., Ledyard 1995). The overall goal of this study is to explore the potential to establish an actual market in which the public can purchase ecosystem services generated by agricultural land. More specifically, this paper evaluates the performance of alternative elicitation methods that are intended to reduce individuals incentives to free-ride on others payments for ecosystem services. Using a choice experiment involving a large-scale mail survey, we first estimate the marginal rate of substitution consumers place on various attributes of farmland including the ecosystem services such land can provide. We further compare the results across different payment mechanisms and examine which ones are capable of revealing demand that is closer to consumers true value. Second, we attempt to establish an actual market in which individuals are asked to purchase a share of a farm contract to provide ecosystem service with real money under different payment mechanisms. We compare the market outcomes with the choice experiments. To the best of our knowledge, this is the first study to examine the performance of different payment mechanisms for provision of ecosystem services using field experiments both within a hypothetical setting and by developing an actual market. The ecosystem service in question in this study is habitat for a grassland-nesting bird called the Bobolink (Dolichonyx oryivorus). Yellow and black Bobolinks establish ground nests in hay fields from mid-May into early June. Their visibility and entertaining character, combined with evidence that many birds, including bobolinks, are experiencing population declines (Sauer et al. 2004), make the bird a leading candidate to attract public interest in efforts to manage farmland for vulnerable wildlife. Previous studies have established that hay harvesting conducted during the birds five to six week nesting period is devastating to fledgling success (e.g., Mitchell et al. 2000). A fairly moderate shift in the harvest schedule could provide significant refuge for nesting birds while causing some losses of the quantity and quality of the hay harvested. If a market developed that paid farmers acceptable compensation to protect grassland birds, then farmers would have an incentive to add an ecosystem service to their revenue base while enhancing environmental quality for wildlife. In this study, we compare four payment mechanisms applied in field experiments: 1) voluntary contribution mechanism, 2) provision point with a money-back guarantee and proportional rebate of excess contributions (PPMBG-PR), 3) uniform-price, multi-buyer auction and 4) pivotal mechanism. Voluntary contribution mechanism has no provision point but has a money-back guarantee if enough money is not raised. Under PPMBG-PR, the public good is supplied only if a pre-specified amount of money (the provision point) is raised, and contributors receive their money back if the market fails to raise that amount. Under a multi-buyer auction, everyone who is willing to pay above a certain price will pay a price such that the total sum will be enough to cover the cost for a farmer to change harvest practices. Under a pivotal mechanism only those consumers whose payments make a difference in the provision of the good would pay. The pivotal mechanism is incentive compatible and is used as the baseline. We test the following hypotheses on the WTP, market participation rate and total revenue collection: (1) WTP: Voluntary contribution < Multi-buyer Auction < PPMBG-PR < Pivotal (2) Participation rate: Voluntary contribution < PPMBG-PR < Multi-buyer auction < Pivotal (3) Revenue collection: Pivotal < Voluntary < Multi-buyer auction < PPMBG-PR We perform a large-scale cross-mechanism comparison using two types of field experiments, a survey involving hypothetical questions and a functioning market for an ecosystem service. In the survey, the subjects are randomly assigned to one of the elicitation methods. We posit a hypothetical situation involving a market for contracts with farmers, describe the assigned elicitation method and ask respondents to compare several sets of two alternative farm wildlife contracts, each with five attributes presented in a stated-choice format. One of the attributes is to change the timing of hay harvesting to enhance the success of a specified number of bobolink fledglings on a given size of farm. The survey data were collected in fall of 2006. Survey questionnaires were sent to all of the 2,987 households in Jamestown, Rhode Island. The response rate was about 37% after accounting for undelivered surveys. Although still preliminary, a key result from the choice experiment is that consumers are least willing to pay for farm wildlife contracts under the voluntary contribution mechanism. The payment method that generated the greatest total purchases of farm wildlife contracts was the multi-buyer auction, followed by the pivotal mechanism and PPMBG-PR, respectively. This result suggests that some features of the payment mechanisms (such as setting of a provision point, fairness and a money-back guarantee) encourage consumers to reveal demand that is closer to each consumer true value of the good than the demand revealed by a simple voluntary contribution mechanism in a field experiment using a hypothetical situation. We are currently in the process of launching an ecosystem-service market in Jamestown by establishing actual farm wildlife contracts with farmers and selling shares of those contracts to consumers. The market will be open to the public for two months during March and April, 2007. Each farm wildlife contract will be tied to one or more of the payment mechanisms and whether each contract will remain effective during the breeding season will depend on the market outcome under each mechanism. Consumers will be randomly assigned to one of the elicitation methods. Using market data, we will compare the actual consumer behavior across alternative methods and also to their willingness to pay as estimated in the survey choice experiment.Land Economics/Use,

The reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards difunctional chloroacetamide alkylating agents: Formation of cyclized or bridged products

The reactions of [Pt₂(μ-S)₂(PPh₃)₄] towards some bis(chloroacetamide) alkylating agents have been investigated. Reaction with one mole equivalent of the hydrazine-derived compound ClCH₂C(O)NHNHC(O)CH₂Cl led to the cyclized product [Pt₂{SCH₂C(O)NHNHC(O)CH₂S}(PPh₃)₄]²⁺ which showed two different PPh₃ environments in the ³¹P{1H} NMR spectrum, as a result of non-fluxional behavior of the dithiolate ligand in solution. Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the ortho and para isomers of the phenylenediamine-derived bis(chloroacetamides) ClCH2C(O)NHC6H4NHC(O)CH2Cl gave tetrametallic complexes containing two {Pt₂S₂} moieties spanned by the CH₂C(O)NHC₆H₄NHC(O)CH₂ group. Both the ortho and para isomers were crystallographically characterized; in the ortho isomer there is intramolecular CO=H–N and S•••H–N hydrogen bonding involving the two amide groups

Millimeter and Submillimeter Survey of the R Corona Australis Region

Using a combination of data from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), the Arizona Radio Observatory Kitt Peak 12m telescope and the Arizona Radio Observatory 10m Heinrich Hertz Telescope, we have studied the most active part of the R CrA molecular cloud in multiple transitions of Carbon Monoxide, HCO$^+$ and 870\micron continuum emission. Since R CrA is nearby (130 pc), we are able to obtain physical spatial resolution as high as 0.01pc over an area of 0.16 pc$^2$, with velocity resolution finer than 1 km/s. Mass estimates of the protostar driving the mm-wave emission derived from HCO$^+$, dust continuum emission and kinematic techniques point to a young, deeply embedded protostar of $\sim$0.5-0.75 M$_\odot$, with a gaseous envelope of similar mass. A molecular outflow is driven by this source that also contains at least 0.8 M$_\odot$ of molecular gas with $\sim$0.5 L$_\odot$ of mechanical luminosity. HCO$^+$ lines show the kinematic signature of infall motions as well as bulk rotation. The source is most likely a Class 0 protostellar object not yet visible at near-IR wavelengths. With the combination of spatial and spectral resolution in our data set, we are able to disentangle the effects of infall, rotation and outflow towards this young object.Comment: 29 pages, 9 figures. Accepted for publication in the Astrophysical Journa

Causes of congenital corneal opacities and their management in a tertiary care center.

PURPOSE: To evaluate causes and management of congenital corneal opacities (CCO) diagnosed in a tertiary care eye center and to compare the data with a previous study at the same institution. METHODS: Computerized medical records in all patients with congenital corneal opacities diagnosed in the Cornea Service at Wills Eye Hospital (Philadelphia, PA) between January 1, 2007, and December 31, 2015, were retrospectively reviewed. Children aged 12 years and younger at the first visit were included in the study. Patients\u27 demographics, ocular diagnosis, laterality, associated ocular abnormalities, other ocular surgery performed prior or subsequent to the first visit, and their treatment were extracted from the medical records. RESULTS: A total of 77 eyes in 56 patients were examined. The mean age at presentation was 32.8 ± 44.2 months, with the mean follow-up period of 26.7 ± 30.1 months. The most frequent diagnosis was Peters anomaly (53.2%), followed by limbal dermoid (13.0%), aniridia with glaucoma and microphthalmos (6.5%), sclerocornea and congenital glaucoma (5.2%), idiopathic (3.9%), Axenfeld-Rieger anomaly and Hurler syndrome (2.6%), and microcornea (1.3%). Primary keratoplasty was performed in 26 eyes, with the outcome rate in the clear cornea of 76.0% during the follow-up. CONCLUSION: Peters anomaly is the most common cause of congenital corneal opacities encountered at our institution. Penetrating keratoplasty is the most frequent choice of corneal surgery to treat congenital corneal opacities. Additional interventions during penetrating keratoplasty were moderately positively correlated with graft failure. This study also shows the rates of some etiologies of that changed over the recent decades in our tertiary care Cornea Service. Although Peters anomaly remains the most common presenting reason for congenital corneal opacities, its rate appears to be increasing over the recent decade. Congenital corneal opacities due to birth trauma, which is one of the preventable causes, were observed in a previous study in our clinic; however, no new cases were noted in this study