969 resultados para Journal articles


Relevância:

60.00% 60.00%

Publicador:

Resumo:

Using survey methodology, a cross sectional study was undertaken to ascertain whether first and fourth year college women have different perceptions and behavior associated with short term mating preferences. It was hypothesized that after incurring significant negative or costly experiences associated with hooking up, fourth year women would prefer men who had qualities associated with a desired long term partner as opposed to characteristics associated with short term mating partners. The results were partially consistent with the hypothesis. Reported preferences in a desired partner and perspective on hooking up differ between first and fourth year groups. No difference was found between frequency and willingness to hookup between the two groups. The findings are explained in terms of evolutionary theory, social exchange theory, and sexual script concepts.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

In the current research, we assessed the impact of parent-child relationships on attitudes toward, and engagement in, hookup behaviors using a sample of 407 college students. Based on prior research, it was hypothesized that heterosexual participants, especially women, who do not perceive themselves as having a strong, close, positive relationship with their opposite-sex parent would be more likely to engage in or attempt to engage in casual sexual behavior (hookups). Also, men were expected to be more satisfied with, and more in agreement with, hookup behavior than women. The results were partially consistent with the hypotheses. Men were more satisfied with and more in agreement with hookup behavior than women. But, opposite sex parent-child relationship quality only affected men’s agreement with the hookup behavior of their peers. Men with lower relationship quality with their mothers agreed more with the hookup behavior of their peers. These results are discussed in relation to prior research on hooking up and prior research on parent-child relationships.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Two new HgCl2 complexes of tridentate nitrogen ligands were characterized by X-ray crystallography, proton NMR spectroscopy and ESI-MS. The five-coordinate complex [Hg(BMPA)Cl-2] (1) (BMPA = bis(2-pyridylmethyl)amine) crystallized from acetonitrile/m-xylene by slow evaporation in the monoclinic space group P2(1)/n with a = 8.3896(8) , b = 12.8020(13) , c = 13.3526(13) , alpha = 90A degrees, beta A = 90.480(2)A degrees, gamma A = 90A degrees and z = 4. The square pyramidal structure (tau = 0.009) has approximate C (s) symmetry. Despite comparable Hg-N bond lengths in 1, inversion of the central nitrogen was rapid on the chemical shift time scale in dilute solution except at very low temperatures. The related complex [Hg(BEPA)Cl-2] (2) (BEPA = bis(2-{pyrid-2-yl}ethyl)amine) crystallized from acetonitrile/ethyl acetate/hexanes by slow diffusion in the orthorhombic space group Pnma with a = 13.424(3) , b = 14.854(3) , c = 8.118(2) , alpha = 90A degrees, beta A = 90A degrees, gamma A = 90A degrees and z = 4. The mixed geometry structure (tau = 0.56) also has crystallographic mirror symmetry as well as C (s) point group symmetry. In dilute acetonitrile solution, 1 was stable while 2 slowly converted to a more thermodynamically stable complex.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Aims: To determine whether or not a Learning Disability(LD) label leads to stigmatization. Study Design: This research used a 2(sex of participant) x 2(LD label)x 2 (Sex of stimulus person) factorial design. Place and Duration of Study: Bucknell University, between October 2010 and April 2011. Methodology: Sample: We included 200 participants (137 women and 63 men, ranging in age from 18 – 75 years, M = 26.41. Participants rated the stimulus individual on 27 personality traits, 8 Life success measures, and the Big-5 personality dimensions. Also, participants completed a Social Desirability measure. Results: A MANOVA revealed a main effect for the Learning Disability description, F(6, 185) = 6.41 p< .0001, eta2 = .17,for the Big-5 personality dimensions, Emotional Stability, F(1, 185) = 13.39, p < .001, eta2 = .066, and Openness to Experiences F(1,185) = 7.12, p< .008, eta2 = .036.Stimulus individuals described as having a learning disability were perceived as being less emotionally stable and more open to experiences than those described as not having a learning disability. Another MANOVA revealed a main effect for having a disability or not, F(8, 183) = 4.29, p< .0001, eta2 = .158, for the Life Success items, Attractiveness, F(1, 198) = 16.63, p< .0001, eta2 = .080, and Future Success,F(1, 198) = 4.57, p< .034, eta2 = .023. Stimulus individuals described as having a learning disability were perceived as being less attractive and with less potential for success than those described as not having a learning disability. Conclusion: The results of this research provide evidence that a bias exists toward those who have learning disabilities. The mere presence of an LD label had the ability to cause a differential perception of those with LDs and those without LDs.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

We describe and analyze the efficiency of a new solar-thermochemical reactor concept, which employs a moving packed bed of reactive particles produce of H2 or CO from solar energy and H2O or CO2. The packed bed reactor incorporates several features essential to achieving high efficiency: spatial separation of pressures, temperature, and reaction products in the reactor; solid–solid sensible heat recovery between reaction steps; continuous on-sun operation; and direct solar illumination of the working material. Our efficiency analysis includes material thermodynamics and a detailed accounting of energy losses, and demonstrates that vacuum pumping, made possible by the innovative pressure separation approach in our reactor, has a decisive efficiency advantage over inert gas sweeping. We show that in a fully developed system, using CeO2 as a reactive material, the conversion efficiency of solar energy into H2 and CO at the design point can exceed 30%. The reactor operational flexibility makes it suitable for a wide range of operating conditions, allowing for high efficiency on an annual average basis. The mixture of H2 and CO, known as synthesis gas, is not only usable as a fuel but is also a universal starting point for the production of synthetic fuels compatible with the existing energy infrastructure. This would make it possible to replace petroleum derivatives used in transportation in the U.S., by using less than 0.7% of the U.S. land area, a roughly two orders of magnitude improvement over mature biofuel approaches. In addition, the packed bed reactor design is flexible and can be adapted to new, better performing reactive materials.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Solar energy is the most abundant persistent energy resource. It is also an intermittent one available for only a fraction of each day while the demand for electric power never ceases. To produce a significant amount of power at the utility scale, electricity generated from solar energy must be dispatchable and able to be supplied in response to variations in demand. This requires energy storage that serves to decouple the intermittent solar resource from the load and enables around-the-clock power production from solar energy. Practically, solar energy storage technologies must be efficient as any energy loss results in an increase in the amount of required collection hardware, the largest cost in a solar electric power system. Storing solar energy as heat has been shown to be an efficient, scalable, and relatively low-cost approach to providing dispatchable solar electricity. Concentrating solar power systems that include thermal energy storage (TES) use mirrors to focus sunlight onto a heat exchanger where it is converted to thermal energy that is carried away by a heat transfer fluid and used to drive a conventional thermal power cycle (e.g., steam power plant), or stored for later use. Several approaches to TES have been developed and can generally be categorized as either thermophysical (wherein energy is stored in a hot fluid or solid medium or by causing a phase change that can later be reversed to release heat) or thermochemical (in which energy is stored in chemical bonds requiring two or more reversible chemical reactions).

Relevância:

60.00% 60.00%

Publicador:

Resumo:

We present a mechanistic modeling methodology to predict both the percolation threshold and effective conductivity of infiltrated Solid Oxide Fuel Cell (SOFC) electrodes. The model has been developed to mirror each step of the experimental fabrication process. The primary model output is the infiltrated electrode effective conductivity which provides results over a range of infiltrate loadings that are independent of the chosen electronically conducting material. The percolation threshold is utilized as a valuable output data point directly related to the effective conductivity to compare a wide range of input value choices. The predictive capability of the model is demonstrated by favorable comparison to two separate published experimental studies, one using strontium molybdate and one using La0.8Sr0.2FeO3-δ as infiltrate materials. Effective conductivities and percolation thresholds are shown for varied infiltrate particle size, pore size, and porosity with the infiltrate particle size having the largest impact on the results.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Rats learn to prefer flavors that are followed by postingestive effects of nutrients. This experiment investigated whether the timing of a flavor (specifically, in the first or second half of the meal) influences learning about that flavor. Stronger learning about earlier or later flavorswould indicate when the rewarding postingestive effects of nutrients are sensed. Ratswith intragastric (IG) catheters drank saccharin-sweetened, calorically-dilute solutions with distinct flavors added, accompanied by IG infusion of glucose (+sessions) or water (−sessions). In both types of sessions, an “Early” flavorwas provided for the first 8 min and a “Late” flavor for the last 8 min. Thus, rats were trained with Early(+) and Late(+) in high-caloriemeals, and Early(−) and Late(−) in low-calorie meals. Strength of the learned preference for Early(+) and Late(+) was then assessed in a series of two-bottle choice tests between Early(+) vs. Early(−), Late(+) vs. Late(−), Early(+) vs. Late(+), and Early(−) vs. Late(−). Rats preferred both Early(+) and Late(+) over the respective (−) flavors. But Early(+)was only preferredwhen rats were tested hungry. Late(+) was preferred when rats were tested hungry or recently satiated. This indicates qualitatively different associations learned about flavors at different points in themeal.While not supporting the idea that postingestive effects become most strongly associated with later-occurring (“dessert”) flavors, it does suggest a reason dessert flavors may remain attractive in the absence of hunger.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

The goal of this article is to explore the various ways that superintendents have responded to accountability-based educational reform efforts such as No Child Left Behind, the factors that have influenced their responses, and the implications of these responses for current and future educational leaders. With respect to the first issue, empirical data from a number of nationai studies (T. E. Glass & Franceschini, 2007; Johnson, Arumi, & Ott, 2006; Johnstone, Dilkkers, & Luedeke, 2009; Stecher et al., 2008) make clear that while there have been a variety of responses from superintendents to accountability-based reform efforts, superintendents have mostly played a supportive role. Examining the situation more fully suggests that the driving factors behind superintendent support for accountability-based educational reform are complex and are often deeply embedded within the "DNA" of the role of superintendent. This article examines the structure of this DNA by looking at the factors that influence superintendents' views of accountability-based educational reform from historical, political, and institutional perspectives. This muitifaceted approach provides new insights into the complex relationship that exists between the structure of the role of superintendent and the agency of the individuals who inhabit that role.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

An often-overlooked aspect of neural plasticity is the plasticity of neuronal composition, in which the numbers of neurons of particular classes are altered in response to environment and experience. The Drosophila brain features several well-characterized lineages in which a single neuroblast gives rise to multiple neuronal classes in a stereotyped sequence during development. We find that in the intrinsic mushroom body neuron lineage, the numbers for each class are highly plastic, depending on the timing of temporal fate transitions and the rate of neuroblast proliferation. For example, mushroom body neuroblast cycling can continue under starvation conditions, uncoupled from temporal fate transitions that depend on extrinsic cues reflecting organismal growth and development. In contrast, the proliferation rates of antennal lobe lineages are closely associated with organismal development, and their temporal fate changes appear to be cell-cycle dependent, such that the same numbers and types of uniglomerular projection neurons innervate the antennal lobe following various perturbations. We propose that this surprising difference in plasticity for these brain lineages is adaptive, given their respective roles as parallel processors versus discrete carriers of olfactory information.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

In this article, I explore how immigrants from the West African nation of Guinea-Bissau living in Portugal use mobile phones in their daily lives in Lisbon. Whereas one might assume that mobile phones and other new information technologies facilitate transnational communication between Africa and Portugal, the ethnographic fieldwork that I conducted in Lisbon from 1999 to 2003 revealed a different scenario. Instead, mobile phones as imagined and used by the Guinean immigrants I met in Lisbon revealed less about transnationalism and globalization than they did about constructing community and identity in a new locale. As Guinean immigrants in Portugal reconfigured their relationship to their former colonizers and struggled to make their way in a new, multicultural Europe, they used their mobile phones to engage local networks, shape local identities, and transform Lisbon's sprawl into an African migrant village. Here, I highlight the gendered dimensions of this process and contend that Guinean men's and women's varied uses of mobile phones in Lisbon underscore contrasting experiences of migration, mobility, and belonging.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

Extraction of natural gas by hydraulic fracturing of the Middle Devonian Marcellus Shale, a major gas-bearing unit in the Appalachian Basin, results in significant quantities of produced water containing high total dissolved solids (TDS). We carried out a strontium (Sr) isotope investigation to determine the utility of Sr isotopes in identifying and quantifying the interaction of Marcellus Formation produced waters with other waters in the Appalachian Basin in the event of an accidental release, and to provide information about the source of the dissolved solids. Strontium isotopic ratios of Marcellus produced waters collected over a geographic range of ∼375 km from southwestern to northeastern Pennsylvania define a relatively narrow set of values (εSr SW = +13.8 to +41.6, where εSr SW is the deviation of the 87Sr/86Sr ratio from that of seawater in parts per 104); this isotopic range falls above that of Middle Devonian seawater, and is distinct from most western Pennsylvania acid mine drainage and Upper Devonian Venango Group oil and gas brines. The uniformity of the isotope ratios suggests a basin-wide source of dissolved solids with a component that is more radiogenic than seawater. Mixing models indicate that Sr isotope ratios can be used to sensitively differentiate between Marcellus Formation produced water and other potential sources of TDS into ground or surface waters.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

We present a new approach for corpus-based speech enhancement that significantly improves over a method published by Xiao and Nickel in 2010. Corpus-based enhancement systems do not merely filter an incoming noisy signal, but resynthesize its speech content via an inventory of pre-recorded clean signals. The goal of the procedure is to perceptually improve the sound of speech signals in background noise. The proposed new method modifies Xiao's method in four significant ways. Firstly, it employs a Gaussian mixture model (GMM) instead of a vector quantizer in the phoneme recognition front-end. Secondly, the state decoding of the recognition stage is supported with an uncertainty modeling technique. With the GMM and the uncertainty modeling it is possible to eliminate the need for noise dependent system training. Thirdly, the post-processing of the original method via sinusoidal modeling is replaced with a powerful cepstral smoothing operation. And lastly, due to the improvements of these modifications, it is possible to extend the operational bandwidth of the procedure from 4 kHz to 8 kHz. The performance of the proposed method was evaluated across different noise types and different signal-to-noise ratios. The new method was able to significantly outperform traditional methods, including the one by Xiao and Nickel, in terms of PESQ scores and other objective quality measures. Results of subjective CMOS tests over a smaller set of test samples support our claims.

Relevância:

60.00% 60.00%

Publicador:

Resumo:

In-stream structures including cross-vanes, J-hooks, rock vanes, and W-weirs are widely used in river restoration to limit bank erosion, prevent changes in channel gradient, and improve aquatic habitat. During this investigation, a rapid assessment protocol was combined with post-project monitoring data to assess factors influencing the performance of more than 558 in-stream structures and rootwads in North Carolina. Cross-sectional survey data examined for 221 cross sections from 26 sites showed that channel adjustments were highly variable from site to site, but approximately 60 % of the sites underwent at least a 20 % net change in channel capacity. Evaluation of in-stream structures ranging from 1 to 8 years in age showed that about half of the structures were impaired at 10 of the 26 sites. Major structural damage was often associated with floods of low to moderate frequency and magnitude. Failure mechanisms varied between sites and structure types, but included: (1) erosion of the channel bed and banks (outflanking); (2) movement of rock materials during floods; and (3) burial of the structures in the channel bed. Sites with reconstructed channels that exhibited large changes in channel capacity possessed the highest rates of structural impairment, suggesting that channel adjustments between structures led to their degradation of function. The data question whether currently used in-stream structures are capable of stabilizing reconfigured channels for even short periods when applied to dynamic rivers.