Statistical investigation of a sample survey for obtaining farm facts

1. A number of the problems of sampling farm facts by means of two sample surveys taken in Iowa have been studied statistically. These were essentially problems of sampling efficiency and the detection and measurement of biases and other errors in the data. 2. A sample survey of 800 farms provided estimates for the state of Iowa which were in many cases as accurate or even more accurate than corresponding information provided by the Federal Census, Iowa State Farm Census or Federal Agricultural Marketing Service. On the other hand, it was found that some items cannot be accurately estimated from a small (800 farm) sample survey, but these items are in many cases only of minor importance. 3. The sampling methods used in these experimental surveys were found to be not only relatively free of bias but also satisfactorily efficient. Certain modifications, however, have been recommended. Some principles have been suggested for modifying size of sampling unit for maximum efficiency when certain cost situations are given. Another feature of the sampling method is that it provides a basis for making unbiased estimates of total number of farms and total land in farms in any desired area and, therefore, is independent of any other source of information. 4. It has been found that wide geographical distribution of sampling units (that is, geographical stratification into small areas) Substantially reduces sampling error. Stratification by tenure group would bring only small gains if any. 5. A method has been proposed for determining the best size of sampling unit for given cost situations and for given expenditure levels. It was concluded that the quarter-section grid is an efficient sampling unit under widely varying circumstances. For investigations requiring very short interviews the half-section grid appears to have important advantages. For general inquiries (such as the census, for example), large blocks such as townships appear to be very inefficient sampling units. 6. Matching samples has proved to be an efficient method of measuring differences between years. Compared with samples taken independently each year, matched samples are from 2.5 to over 20 times as efficient, depending upon the item

Pioneer 10 and Voyager observations of the interstellar medium in scattered emission of the He584 A and H Lya 1216 A lines

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 A was applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments in the same way as other earlier determinations based on the same method. However, the spacecraft data were combined with daily full sun averages of the H Lyman 1216 A line obtained by the Solar Mesospheric Explorer satellite to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a one year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are H = 0.12 cu cm and H = .016 cu cm, giving a density ratio close to the cosmic abundance value in contrast to some earlier results indicating a depletion of atomic hydrogen. Estimates were obtained of galactic background emissions in the signals of both spacecraft

A lattice of double wells for manipulating pairs of cold atoms

We describe the design and implementation of a 2D optical lattice of double wells suitable for isolating and manipulating an array of individual pairs of atoms in an optical lattice. Atoms in the square lattice can be placed in a double well with any of their four nearest neighbors. The properties of the double well (the barrier height and relative energy offset of the paired sites) can be dynamically controlled. The topology of the lattice is phase stable against phase noise imparted by vibrational noise on mirrors. We demonstrate the dynamic control of the lattice by showing the coherent splitting of atoms from single wells into double wells and observing the resulting double-slit atom diffraction pattern. This lattice can be used to test controlled neutral atom motion among lattice sites and should allow for testing controlled two-qubit gates.Comment: 9 pages, 11 figures Accepted for publication in Physical Review

TGF beta type II receptor signaling controls Schwann cell death and proliferation in developing nerves

During development, Schwann cell numbers are precisely adjusted to match the number of axons. It is essentially unknown which growth factors or receptors carry out this important control in vivo. Here, we tested whether the type II transforming growth factor (TGF)beta receptor has a role in this process. We generated a conditional knock-out mouse in which the type II TGF beta receptor is specifically ablated only in Schwann cells. Inactivation of the receptor, evident at least from embryonic day 18, resulted in suppressed Schwann cell death in normally developing and injured nerves. Notably, the mutants also showed a strong reduction in Schwann cell proliferation. Consequently, Schwann cell numbers in wild-type and mutant nerves remained similar. Lack of TGF beta signaling did not appear to affect other processes in which TGF beta had been implicated previously, including myelination and response of adult nerves to injury. This is the first in vivo evidence for a growth factor receptor involved in promoting Schwann cell division during development and the first genetic evidence for a receptor that controls normal developmental Schwann cell death

Detrimental adsorbate fields in experiments with cold Rydberg gases near surfaces

We observe the shift of Rydberg levels of rubidium close to a copper surface when atomic clouds are repeatedly deposited on it. We measure transition frequencies of rubidium to S and D Rydberg states with principal quantum numbers n between 31 and 48 using the technique of electromagnetically induced transparency. The spectroscopic measurement shows a strong increase of electric fields towards the surface that evolves with the deposition of atoms. Starting with a clean surface, we measure the evolution of electrostatic fields in the range between 30 and 300 \mum from the surface. We find that after the deposition of a few hundred atomic clouds, each containing ~10^6 atoms, the field of adsorbates reaches 1 V/cm for a distance of 30 \mum from the surface. This evolution of the electrostatic field sets serious limitations on cavity QED experiments proposed for Rydberg atoms on atom chips.Comment: 4 pages, 3 figures Submitted to Phys. Rev.

Statistical investigations of farm sample surveys taken in Iowa, Florida and California

The object of this bulletin is to present results of statistical analyses of data from recent sample surveys of agricultural areas and to offer some comments on the sampling procedures followed. The surveys described herein were made in widely differing farming areas: In all of the 99 counties of Iowa, in 26 of the 67 counties in Florida, and in 9 of the 58 counties of California. Except for Iowa (3) these surveys were pioneering a sampling method in their respective areas. In order to observe the way in which this method behaved in different parts of the country we have brought the findings together under one cover

Some investigations on the suitability of the township as a unit for sampling Iowa agriculture

The purpose of this study was to determine a sampling procedure by which agricultural information may be efficiently obtained for areas smaller than the state, particularly the county. This study, therefore, is one of a series (2) (4) directed toward the problems of methodology of an agricultural sample-census. The objectives (8) of such a sample-census are: To obtain useful information (a) more frequently (annually instead of quinquennially, as at present), (b) of greater extent (include items not covered by the regular census) and (c) at greater economy. Consequently the sample-census is proposed at least in part to supplement the regular census in providing the information needed in the analysis and understanding of special agricultural problems arising in the field of policy and programs, such as farm tenancy, soil conservation, etc. This study, however, is limited to an investigation of merely a few of the many problems of sample-census procedure. Here we are interested primarily in the following questions: 1. Is it possible to find a township or group of townships within a county which will satisfactorily represent that county for a period of years? 2. For a given degree of accuracy, how large must a sample he for (a) a county, (b) a crop-reporting district (a group of about 10 counties)? 3. Are there any satisfactory criteria by which a county may be stratified and thereby increase sampling efficiency? This study provides, we believe, some aid in answering these and allied questions

Bloch Structures in a Rotating Bose-Einstein Condensate

A rotating Bose-Einstein condensate is shown to exhibit a Bloch band structure without the need of periodic potential. Vortices enter the condensate by a mechanism similar to the Bragg reflection, if the frequency of a rotating drive or the strength of interaction is adiabatically changed. A localized state analogous to a gap soliton in a periodic system is predicted near the edge of the Brillouin zone.Comment: 4 pages, 3 figure

Quantum computing with spatially delocalized qubits

We analyze the operation of quantum gates for neutral atoms with qubits that are delocalized in space, i.e., the computational basis states are defined by the presence of a neutral atom in the ground state of one out of two trapping potentials. The implementation of single qubit gates as well as a controlled phase gate between two qubits is discussed and explicit calculations are presented for rubidium atoms in optical microtraps. Furthermore, we show how multi-qubit highly entangled states can be created in this scheme.Comment: 4 pages, 4 figure