Apollo oxygen tank stratification analysis, volume 2

An analysis of flight performance of the Apollo 15 cryogenic oxygen tanks was conducted with the variable grid stratification math model developed earlier in the program. Flight conditions investigated were the CMP-EVA and one passive thermal control period which exhibited heater temperature characteristics not previously observed. Heater temperatures for these periods were simulated with the math model using flight acceleration data. Simulation results (heater temperature and tank pressure) compared favorably with the Apollo 15 flight data, and it was concluded that tank performance was nominal. Math model modifications were also made to improve the simulation accuracy. The modifications included the addition of the effects of the tank wall thermal mass and an improved system flow distribution model. The modifications improved the accuracy of simulated pressure response based on comparisons with flight data

Fluctuations of the Casimir-Polder force between an atom and a conducting wall

We consider the quantum fluctuations of the Casimir-Polder force between a neutral atom and a perfectly conducting wall in the ground state of the system. In order to obtain the atom-wall force fluctuation we first define an operator directly associated to the force experienced by the atom considered as a polarizable body in an electromagnetic field, and we use a time-averaged force operator in order to avoid ultraviolet divergences appearing in the fluctuation of the force. This time-averaged force operator takes into account that any measurement involves a finite time. We also calculate the Casimir-Polder force fluctuation for an atom between two conducting walls. Experimental observability of these Casimir-Polder force fluctuations is also discussed, as well as the dependence of the relative force fluctuation on the duration of the measurement.Comment: 6 page

A possible intermediate step in the reorganization of rural elementary education in Iowa

Iowa has a very large number of small rural school districts. Of the 4,870 school corporations in the state, 2,807 are rural independent districts and 1,010 are school townships. There are in the state 12,279 public schools of all types, including kindergartens, rural schools, elementary schools (not rural) and high schools. Of this number, 9,223, or about 75 percent, are one-room rural schools. With one exception the number of such schools in Iowa exceeds that found in any other state. The average enrollment in the one-room rural schools of the state in 1932-33 was only 15.8 students; the average daily attendance was 12.6. These ungraded rural schools of the state enrolled 29 percent of the entire number of pupils but employed 38 percent of the teachers. The first class cities, on the other hand, enrolled 23 percent of the pupils of the state but employed only 16 percent of the teachers. The town and consolidated schools, as a rule, also have small total enrollments and small enrollments per teacher. Before the depression the average salary of teachers of one-room rural schools in Iowa was $722 per year, while that of city elementary teachers was$1,573 per year. When the depression brought a demand for reducing expenses, the rural teacher\u27s wage was cut approximately 35 percent, to $465 per year, and the city elementary teacher\u27s wage was reduced 19 percent, to$1,271 per year. From the foregoing it follows that rural people, in general, may have only teachers of inferior training for their children. Yet, in many instances, the per-pupil cost of such instruction is actually higher than that in the elementary grades of city schools; and it appears, on the whole, that there is no great difference in the per-pupil cost of elementary instruction in the two types of schools. This condition clearly reveals the handicap which children face who are born and reared in the country. Moreover a disadvantage also seems to have fallen upon their parents, whose per capita income, even in normal times, is apparently not more than half of that of the non-farm population. Not only must they accept inferior educational opportunities for their children, but they must pay for such facilities a sum more than twice as much, in relation to their incomes, as that paid by people not living in the country. So far no satisfactory solution has been suggested for the problem of how to provide education for rural children that is equal in quality to that which is generally available to the non-farm children of Iowa. Yet with the establishment of the many graded school systems during the past 3 or 4 decades, and with the more recent improvement of the roads of the state, it has seemed that an acceptable solution was gradually becoming possible. In fact, for some time there has been reason to believe that not nearly all of the one-room schools being maintained in Iowa are really needed; many children attending a considerable number of them apparently could be transported to nearby graded school systems and educated at a total cost actually no greater than that being paid at present, provided the patrons of such one-room schools desired to do so. lf arrangements could be made, therefore, whereby the rural and non-rural children of Iowa would attend the same schools they would enjoy more nearly equal educational advantages and opportunities. To remove the present educational handicap of all rural children of Iowa in this manner, however, would entail a considerable increase in educational costs.1 For how many of them it might be removed without additional cost has been determined for a considerable part of the state in connection with an investigation, the results of which are reported in the following pages. Nothing presented in this bulletin, however, suggests any changes in the existing school systems, other than those which would and could at present be taken purely upon local initiative

Ultra-high-sensitivity two-dimensional bend sensor

A multicore fibre Fabry-Perot-based strain sensor interrogated with tandem interferometry for bend measurement is described. Curvature in two dimensions is obtained by measuring the difference in strain between three co-located low finesse Fabry-Perot interferometers formed in each core of the fibre by pairs of Bragg gratings. This sensor provides a responsivity enhancement of up to 30 times that of a previously reported fibre Bragg grating based sensor. Strain resolutions of 0.6 n epsilon/Hz(1/2) above 1 Hz are demonstrated, which corresponds to a curvature resolution of similar to 0.012 km(-1)/Hz(1/2)

Computational Efficiency of Frequency-- and Time--Domain Calculations of Extreme Mass--Ratio Binaries: Equatorial Orbits

Gravitational waveforms and fluxes from extreme mass--ratio inspirals can be computed using time--domain methods with accuracy that is fast approaching that of frequency--domain methods. We study in detail the computational efficiency of these methods for equatorial orbits of fast spinning Kerr black holes, and find the number of modes needed in either method --as functions of the orbital parameters-- in order to achieve a desired accuracy level. We then estimate the total computation time and argue that for high eccentricity orbits the time--domain approach is more efficient computationally. We suggest that in practice low--$m$ modes are computed using the frequency--domain approach, and high--$m$ modes are computed using the time--domain approach, where $m$ is the azimuthal mode number.Comment: 19 figures, 6 table

`Operational' Energy Conditions

I show that a quantized Klein-Gordon field in Minkowski space obeys an `operational' weak energy condition: the energy of an isolated device constructed to measure or trap the energy in a region, plus the energy it measures or traps, cannot be negative. There are good reasons for thinking that similar results hold locally for linear quantum fields in curved space-times. A thought experiment to measure energy density is analyzed in some detail, and the operational positivity is clearly manifested. If operational energy conditions do hold for quantum fields, then the negative energy densities predicted by theory have a will-o'-the-wisp character: any local attempt to verify a total negative energy density will be self-defeating on account of quantum measurement difficulties. Similarly, attempts to drive exotic effects (wormholes, violations of the second law, etc.) by such densities may be defeated by quantum measurement problems. As an example, I show that certain attempts to violate the Cosmic Censorship principle by negative energy densities are defeated. These quantum measurement limitations are investigated in some detail, and are shown to indicate that space-time cannot be adequately modeled classically in negative energy density regimes.Comment: 18 pages, plain Tex, IOP macros. Expanded treatment of measurement problems for space-time, with implications for Cosmic Censorship as an example. Accepted by Classical and Quantum Gravit

Functionalized Rhodium Intercalators for DNA Recognition

A series of rhodium complexes containing the phenanthrenequinone diimine (phi) ligand have been prepared which bind DNA by intercalation and, upon photoactivation, promote DNA strand breaks. In this series, the ancillary, nonintercalating bipyridyl or phenanthroline ligands have been functionalized to yield complexes containing guanidinium, amido, or amino groups arranged with defined stereochemistry for site-specific interaction with the DNA bases. Λ-1-[Rh(MGP)_2phi]^(5+) (MGP = 4-(guanidylmethyl)-1,10-phenanthroline) site-specifically targets the 6-base pair sequence 5‘-CATATG-3‘ with a binding affinity of 1 (±0.5) × 10^8 M^(-1) while Δ-1-[Rh(MGP)_2phi]^(5+) displays an affinity of 5 (±2) × 10^7 M^(-1) for 5‘-CATCTG-3‘. Even though these two isomers target sites which differ by only a single base, binding is highly enantioselective. The specificity is derived chiefly from interactions of the pendant guanidinium groups with the DNA bases. For the racemates of 1-[Rh(GEB)_2phi]^(5+) (GEB = (4-(2-guanidylethyl)-4‘-methyl-2,2‘-bipyridine) and 1-[Rh(GPB)_2phi]^(5+) (GPB = (4-(2-guanidylpropyl)-4‘-methyl-2,2‘-bipyridine), photocleavage patterns also show the strongest site of photocleavage as 5‘-CATCTG-3‘, the target site for Δ-1-[Rh(MGP)_2phi]^(5+). Moreover, consistent with the dominance of the guanidinium groups in establishing specificity, significantly enhanced photocleavage is evident for the 1-positional isomer of these complexes, where the guanidinium moieties are directed toward the DNA (above and below the phi ligand) compared to the 2-isomer, in which the guanidinium groups are directed away from the DNA. In contrast to Λ-1-[Rh(MGP)_2phi]^(5+), Λ-1-[Rh(GEB)_2phi]^(5+) shows little cleavage at 5‘-CATATG-3‘; this sensitivity to linker length likely depends on the mode of recognition of 5‘-CATATG-3‘ involving sequence-dependent unwinding of the DNA site. Analogous site-specificity or isomer-specificity is not evident with the complexes which contain pendant amido or amino functionalities. Instead these complexes appear to resemble the parent, unfunctionalized [Rh(phen)_2phi]^(3+) with respect to recognition. Pendant guanidinium functionalities appear to be particularly advantageous in the construction of small molecules which bind DNA with site-specificity