Interplanetary Trajectory Optimization with Powerlimited Propulsion Systems

A trajectory-optimization process is described in which the optimum thrust equations are derived using the calculus of variations. The magnitude of the thrust is constrained within an upper and a lower bound, but the thrust direction is arbitrary. This formulation allows both the constant-thrust program and the variable-thrust program to be considered. For the constant-thrust program, certain propulsion-system parameters are optimized for maximum final vehicle mass. This theory has been used to study interplanetary missions to Venus and Mars using a power-limited propulsion system. Both one-way and round trip rendezvous trajectories are considered. The analysis employs a two-body inverse-square force-field model of three dimensions. An iterative routine used to solve the two-point boundary-value problem is described in the Appendix

Evaluation of anomalies observed on film from S-190A flight system calibration test

Due to a persistent problem of scratched film from testing of the Skylab S-190A system, a series of tests were designed to identify the cause of the film scratching. The procedures followed in this test for pretest handling and packaging of the film, the makeup of the rolls for processing, and the results of the processed film evaluation are reported

Measurement of the electron electric dipole moment using YbF molecules

The most sensitive measurements of the electron electric dipole moment d_e have previously been made using heavy atoms. Heavy polar molecules offer a greater sensitivity to d_e because the interaction energy to be measured is typically 10^3 times larger than in a heavy atom. We report the first measurement of this kind, for which we have used the molecule YbF. Together, the large interaction energy and the strong tensor polarizability of the molecule make our experiment essentially free of the systematic errors that currently limit d_e measurements in atoms. Our first result d_e = (- 0.2 \pm 3.2) x 10^-26 e.cm is less sensitive than the best atom measurement, but is limited only by counting statistics and demonstrates the power of the method.Comment: 4 pages, 4 figures. v2. Minor corrections and clarifications made in response to referee comment

Unraveling the molecular basis of subunit specificity in P pilus assembly by mass spectrometry

P pili are multisubunit fibers essential for the attachment of uropathogenic Escherichia coli to the kidney. These fibers are formed by the noncovalent assembly of six different homologous subunit types in an array that is strictly defined in terms of both the number and order of each subunit type. Assembly occurs through a mechanism termed “donor-strand exchange (DSE)” in which an N-terminal extension (Nte) of one subunit donates a β-strand to an adjacent subunit, completing its Ig fold. Despite structural determination of the different subunits, the mechanism determining specificity of subunit ordering in pilus assembly remained unclear. Here, we have used noncovalent mass spectrometry to monitor DSE between all 30 possible pairs of P pilus subunits and their Ntes. We demonstrate a striking correlation between the natural order of subunits in pili and their ability to undergo DSE in vitro. The results reveal insights into the molecular mechanism by which subunit ordering during the assembly of this complex is achieved

A Logistic Regression Model For The Enhancement Of Student Retention: The Identification Of At-Risk Freshmen

A logistic regression model will be developed to provide early identification of freshmen at risk of attrition.  The early identification is accomplished literally within a couple of weeks after freshman orientation.  The dependent variable of interest is persistence, and it is a binary, nominal variable.  Students who proceed from freshman matriculation to graduation without ever having dropped out are labeled persistors.  Freshman matriculates who leave college either temporarily or permanently are classified as dropouts.  The independent variables employed to predict attrition include demographics, high school experiences, and attitudes, opinions, and values as reported on a survey administered during freshman orientation.  The model and its results will be presented along with a brief description of the institutional intervention program designed to enhance student persistence

Slowing heavy, ground-state molecules using an alternating gradient decelerator

Cold supersonic beams of molecules can be slowed down using a switched sequence of electrostatic field gradients. The energy to be removed is proportional to the mass of the molecules. Here we report deceleration of YbF, which is 7 times heavier than any molecule previously decelerated. We use an alternating gradient structure to decelerate and focus the molecules in their ground state. We show that the decelerator exhibits the axial and transverse stability required to bring these molecules to rest. Our work significantly extends the range of molecules amenable to this powerful method of cooling and trapping.Comment: 4 pages, 5 figure

A change of the seaward boundary of Goukamma Marine Protected Area could increase conservation and fishery benefits

Goukamma Marine Protected Area (MPA) on the South African temperate South Coast has been shown to be effective in maintaining a spawning stock of roman, Chrysoblephus laticeps (Sparidae). The larval ecology and the oceanographic conditions in the area suggest a good potential for the enhancement of roman stocks outside the reserve through larval dispersal. A high rate of illegal fishing just inside the seaward boundary of the MPA could severely compromise its function.We suggest that a change of the seaward boundary of the reserve to coincide with a latitudinal line could increase its function as a harvest refuge for resident reef fishes such as roman, facilitate voluntary compliance and monitoring and prosecution of illegal fishing without a significant negative impact on the commercial linefishing fleet in the area. Simple adjustments such as the one proposed here could be attempted at a number of South African MPAs as they would be beneficial to achieve fishery and conservation goals alike

Hamiltonian formulation of nonlinear travelling Whistler waves

International audienceA Hamiltonian formulation of nonlinear, parallel propagating, travelling whistler waves is developed. The complete system of equations reduces to two coupled differential equations for the transverse electron speed $u$ and a phase variable $\phi{=}\phi_p-\phi_e$ representing the difference in the phases of the transverse complex velocities of the protons and the electrons. Two integrals of the equations are obtained. The Hamiltonian integral H, is used to classify the trajectories in the $(phi,w)$ phase plane, where $phi$ and w=u2 are the canonical coordinates. Periodic, oscilliton solitary wave and compacton solutions are obtained, depending on the value of the Hamiltonian integral H and the Alfvén Mach number M of the travelling wave. The second integral of the equations of motion gives the position x in the travelling wave frame as an elliptic integral. The dependence of the spatial period, L, of the compacton and periodic solutions on the Hamiltonian integral H and the Alfvén Mach number M is given in terms of complete elliptic integrals of the first and second kind. A solitary wave solution, with an embedded rotational discontinuity is obtained in which the transverse Reynolds stresses of the electrons are balanced by equal and opposite transverse stresses due to the protons. The individual electron and proton phase variables $phi_e$ and $phi_p$ are determined in terms of $phi$ and $w$. An alternative Hamiltonian formulation in which ${\tilde\phi}{=}\phi_p+\phi_e$ is the new independent variable replacing x is used to write the travelling wave solutions parametrically in terms of ${\tilde\phi}$

Persist/Dropout Differences In Pre-matriculation Attitudes Of Freshman Towards College Attrition: A Longitudinal Multiple Group Structural Equations Model

This study proposes a structural equations model of college student attrition based on pre-matriculation freshman attitudes. The study uses a survey administered annually from 1995 to 1999 and tracks persistence and dropout behavior for five years until the last cohort graduated. It discusses seven constructs of pre-matriculation freshman attitudes that resemble the Cabrera, Nora, and Castañeda (1993) model of College Persistence that was based on attitudes of first-to-second year enrolled college students. We applied our survey to a Northeastern sectarian private college. Our model includes external factors such as financial attitude, and endogenous variables such as academic reputation, social integration, institutional commitment, goal commitment, academic performance, and intent to persist. In addition to the variables related to the Cabrera model, we added two measures of social integration, “political interests” and “concern-for the disadvantaged” because these were suitable to the type of college which hosted the study. Results provide a multiple group comparative and predictive model of student attrition for annual use by the Dean of Student Affairs in designing proactive plans and implementing intervention strategies to enhance student retention

A change of the seaward boundary of Goukamma Marine Protected Area could increase conservation and fishery benefits

Goukamma Marine Protected Area (MPA) on the South African temperate South Coast has been shown to be effective in maintaining a spawning stock of roman, Chrysoblephus laticeps (Sparidae). The larval ecology and the oceanographic conditions in the area suggest a good potential for the enhancement of roman stocks outside the reserve through larval dispersal. A high rate of illegal fishing just inside the seaward boundary of the MPA could severely compromise its function. We suggest that a change of the seaward boundary of the reserve to coincide with a latitudinal line could increase its function as a harvest refuge for resident reef fishes such as roman, facilitate voluntary compliance and monitoring and prosecution of illegal fishing without a significant negative impact on the commercial linefishing fleet in the area. Simple adjustments such as the one proposed here could be attempted at a number of South African MPAs as they would be beneficial to achieve fishery and conservation goals alike