Movement of Spermatozoa in Viscous Environments

Observations of the effects of increased viscosity have been important in attempting to understand the mechanical forces and molecular mechanisms involved in cell motility. Berg & Turner (1979) have recently demonstrated that the movement of bacteria at increased viscosities depends on the nature of the macromolecules used to obtain increased viscosities. With methyl cellulose, an unbranched, long-chain polymer, decreases in rotation rates of tethered E. coli were much less than with Ficoll, a highly branched polymer, even though the viscosities measured at the macroscopic level were similar. At the microscopic level, methyl cellulose apparently forms a loose, quasi-rigid network in solution, which is easily penetrated by particles on the scale of bacteria and their flagella, but makes a substantial contribution to the macroscopic viscosity of the solution even at concentrations where 'non-Newtonian' behavior is minimal. This observation has led us to re-examine earlier measurements on the effects of viscosity on the movement of sperm flagella, which were made using methyl cellulose to increase the viscosity (Brokaw, 1966; Brokaw & Simonick, 1977)

Strange Quark Contribution to the Nucleon Spin from Electroweak Elastic Scattering Data

The total contribution of strange quarks to the intrinsic spin of the nucleon can be determined from a measurement of the strange-quark contribution to the nucleon's elastic axial form factor. We have studied the strangeness contribution to the elastic vector and axial form factors of the nucleon, using elastic electroweak scattering data. Specifically, we combine elastic $\nu p$ and $\bar{\nu} p$ scattering cross section data from the Brookhaven E734 experiment with elastic $ep$ and quasi-elastic $ed$ and $e$-$^4$He scattering parity-violating asymmetry data from the SAMPLE, HAPPEx, G0 and PVA4 experiments. We have not only determined these form factors at individual values of momentum-transfer ($Q^2$), but also have fit the $Q^2$-dependence of these form factors using simple functional forms. We present the results of these fits, along with some expectations of how our knowledge of these form factors can be improved with data from Fermilab experiments.Comment: 3 pages, 1 figure, CIPANP 201

Elite CEOs: Impact on Compensation and Firm Performance Models

A particular body of research examines the issue of linking executive pay to firm performance by focusing on the observation that CEO compensation varies widely across firms, even within the same industry. This research assumes that the same compensation model (i.e., structure of the model, explanatory variables, and coefficients on those variables) can be applied to all CEOs. If you will, extant research assumes a one-size-fits-all CEO compensation model approach to empirical analysis. Furthermore, much of this research also examines firm performance and similarly utilizes a one-size-fits-all firm performance model. I develop a proxy for CEO managerial power that I use to rank and classify CEOs into two groups: Elite CEOs (above a cut-off by the ranking) and Non-Elite CEOs (the remaining CEOs). As a note, I demonstrate that ranking the CEOs by my proxy for CEO managerial power is not the same as simply ranking the CEOs by their total direct compensation. My empirical results show that a one-size-fits-all model can be rejected. That is, the estimated coefficients in compensation models and firm performance models are different for Elite CEOs as compared to Non-Elite CEOs. Also, firms with Elite CEOs do not have higher performance. This suggests that Elite CEOs extract excessive compensation due to undue influence over their respective boards rather than to superior performance. These findings have both academic and corporate policy implications

Triple-A Ratings Stench: May the Credit Rating Agencies be Held Accountable?

This article analyzes the role the Credit Rating Agencies (CRAs) played in developing markets for certain types of asset-backed securities in order to identify how the CRAs promoted the leverage build up that occurred over the past 15 years. This analysis will highlight the fundamental flaws in the ratings process, with a view toward being able to assign responsibility accordingly. Further, the motivations of banks, financial institutions, and corporate issuers in relying on the CRAs will be critiqued. Additionally, the principal past and current in-court claims against the CRAs will be analyzed and hypotheses will be drawn on the liability that may await the CRAs for their involvement in assisting the credit crisis. Finally, several proposals for legislative reform will be suggested and conclusions will be offered on the future role CRAs may be expected to play

Comparison of The Production of Bibb Lettuce Reared In Indoor Aquaponics System using Large Mouth Bass (Micropterus salmoides) Vs. Nile Tilapia (Oreochromis niloticus)

Aquaponics is a sustainable food production system that combines hydroponic plant growth with fish rearing in a recirculating aquaculture system. Nile tilapia (Oreochromis niloticus) are predominantly raised in aquaponics due to their fast growth rates and ability to tolerate a variety of water conditions. As aquaponics becomes more popular in temperate climate zones, farmers are looking for alternative fish species that are more compatible with cooler temperatures and have a higher market value than tilapia. Authors will determine if plant growth factors as well as, the availability of nutrients in aquaponic systems are affected by the difference in nutrient requirements among fish species, This study evaluated plant growth factors between aquaponic systems stocked with Nile tilapia and largemouth bass (LMB) (Micropterus salmoides). Six replicate systems were used that included a 415-L fish tank, a 190-L settling tank, a 115-L clarifier, and two 1.5 m2 floating raft beds with a 72 plant capacity. Bibb lettuce (Lactuca sativa) and Red Russian kale (Brassica napus) were evaluated in successive planting cycles. Fish were stocked at approximately 1,400g per system and fed five percent body weight per day. Tilapia and LMB were fed a floating feed containing 32% and 45% protein, respectively. At harvest, total plant biomass in each system was recorded. Sixteen representative samples from each system were also collected and analyzed for plant and root weight, number of leaves, leaf surface area, root/shoot ratio, and chlorophyll content. Representative samples from each system were also dried and analyzed for micro and macro nutrient content. Upon conclusion of this study, researchers will determine if differences exist in plant growth factors between tanks stocked with tilapia and LMB. This information will determine if producers are able to maximize their production and potential profits in aquaponics using LMB

An experimental comparison of evaporation and condensation heat transfer coefficients for HFC-134a and CFC-12

Citation: Eckels, S.J. and M.B. Pate, An experimental comparison of evaporation and condensation heat transfer coefficients for HFC-134a and CFC-12.International Journal of Refrigeration, 1991. 14(2): p. 70-77.Experimental heat transfer coefficients are reported for HFC-134a and CFC-12 during in-tube single-phase flow, evaporation and condensation. These heat transfer coefficients were measured in a horizontal, smooth tube with an inner diameter of 8.0 mm and a length of 3.67 m. The refrigerant in the test-tube was heated or cooled by using water flowing through an annulus surrounding the tube. Evaporation tests were performed for a refrigerant temperature range of 5–15°C with inlet and exit qualities of 10 and 90%, respectively. For condensation tests, the refrigerant temperature ranged from 30 to 50°C, with et and exit qualities of 90 and 10%, respectively. The mass flux was varied from 125 to 400 kg m−2 s−1 for all tests. For similar mass fluxes, the evaporation and condensation heat transfer coefficients for HFC-134a were significantly higher than those of CFC-12. Specifically, HFC-134a showed a 35–45% increase over CFC-12 for evaporation and a 25–35% increase over CFC-12 for condensation. Résumé On rapporte les coefficients de transfert de chaleur expérimentaux, pour le HFC-134a et le CFC-12, au cours d'un écoulement monophasique, à l'intérieur d'un double tube, et au cours de l'évaporation et de la condensation. Ces coefficients de transfert de chaleur ont été mesurés dans un tube lisse horizontal d'un diamètre intérieur de 8 mm et d'une longueur de 3,67 m. Le frigorigène dans le tube d'essai était chauffé ou refroidi par circulation d'eau dans un espace annulaire entourant le tube. Pour l'évaporation, les essais ont été effectués dans une plage de températures du frigorigène comprises entre 5 et 15°C, avec des qualités d'entrée et de sortie de 10 et 90% respectivement. Pour les essais de condensation, les températures du frigorigène étaient comprises entre 30 et 50°C, avec des qualités d'entrée et de sortie de 90 et 10% respectivement. Le flux massique a varié de 125 à 400 kg m−2 s−1 pour tous les essais. Pour des flux massiques similaires, les coefficients de transfert de chaleur d'évaporation et de condensation, pour le HFC-134a, étaient nettement supérieurs à ceux du CFC-12. Plus précisément, le coefficient de transfert de chaleur à l'évaporation du HFC-134a était de 35 à 45% supérieur à celui du CFC-12, et le coefficient de transfert de chaleur à la condensation supérieur de 25 à 35%