On simple endotrivial modules

We show that when G is a finite group which contains an elementary Abelian subgroup of order p^2 and k is an algebraically closed field of characteristic p, then the study of simple endotrivial kG-modules which are not monomial may be reduced to the case when G is quasi-simple

A Holocene paleoenvironmental record based on ungulate stable isotopes from Lukenya Hill, Kenya

Investigating the development of Holocene behavioral adaptations requires knowing how and why different human groups are distributed on the landscape. An expanded dataset of site-specific environmental and habitat reconstructions from eastern Africa are crucial contextual components necessary for pushing this line of inquiry forward. This paper provides localized paleoenvironmental data from Holocene deposits at the multi-site Lukenya Hill archaeological complex on the Athi-Kapiti Plains of Kenya. Lukenya Hill preserves two temporal units, an early-mid Holocene (~9.0–4.6 ka) and a late Holocene (~2.3–1.2 ka), which span the end of the African Humid Period and the onset of late Holocene aridification. Carbon isotope analysis of herbivore tooth enamel (n = 22) indicates an increase in open grasslands over time with the early-mid Holocene having a woodier signal than the late Holocene and Recent populations in the Athi ecosystem. This pattern deviates from local environmental sequences in the Lake Victoria and Lake Turkana basins, providing additional evidence of heterogeneous habitat conditions during the Holocene of eastern Africa. The expansion of locally specific paleoecological datasets in eastern Africa allows for an examination of the role climate and ecology played in human economic and behavioral development during the Holocene.Accepted manuscrip

High amplitude sinusoidal pressure generator

Generator is an inlet-area-modulated, gas-flow-through device utilizing hydrogen gas and a rotating disk for operation. Design enables generator to produce pressure oscillations as high as 120, 18, and 12 percent of the mean chamber pressure at frequencies of 1, 10, and 15 kHz, respectively

Equations of motion in the linear approximation

Gauge invariant theory of motion of singularities in linear approximatio

Open sets satisfying systems of congruences

A famous result of Hausdorff states that a sphere with countably many points removed can be partitioned into three pieces A,B,C such that A is congruent to B (i.e., there is an isometry of the sphere which sends A to B), B is congruent to C, and A is congruent to (B union C); this result was the precursor of the Banach-Tarski paradox. Later, R. Robinson characterized the systems of congruences like this which could be realized by partitions of the (entire) sphere with rotations witnessing the congruences. The pieces involved were nonmeasurable. In the present paper, we consider the problem of which systems of congruences can be satisfied using open subsets of the sphere (or related spaces); of course, these open sets cannot form a partition of the sphere, but they can be required to cover "most of" the sphere in the sense that their union is dense. Various versions of the problem arise, depending on whether one uses all isometries of the sphere or restricts oneself to a free group of rotations (the latter version generalizes to many other suitable spaces), or whether one omits the requirement that the open sets have dense union, and so on. While some cases of these problems are solved by simple geometrical dissections, others involve complicated iterative constructions and/or results from the theory of free groups. Many interesting questions remain open.Comment: 44 page

Dynamic response of high-frequency pressure transducers to large amplitude sinusoidal pressure oscillations

Dynamic response characteristics of six currently used dynamic pressure transducers were investigated by using a large-amplitude sinusoidal-pressure generator. Frequencies between 1 and 15 kilohertz with corresponding peak-to-peak pressure-oscillation amplitudes ranging between 73 and 8 percent of bias pressure and bias pressures between 15 and 300 psia were utilized. Amplitude-ratio data as functions of frequency and pressure level are given for all transducers. The generator design and performance and associated instrumentation are described

Wind-Tunnel Investigation at a Mach Number of 2.01 of the Aerodynamic Characteristics in Combined Angles of Attack and Sideslip of Several Hypersonic Missile Configurations with Various Canard Controls

An investigation of the aerodynamic characteristics of several hypersonic missile configurations with various canard controls for an angle-of-attack range from 0 deg to about 28 deg at sideslip angles of about 0 deg and 4 deg at a Mach number of 2.01 has been made in the Langley 4- by 4-foot supersonic pressure tunnel. The configurations tested we re a body alone which had a ratio of length to diameter of 10, the b ody with a 10 deg flare, the body with cruciform fins of 5 deg or 15 deg apex angle, and a flare-stabilized rocket model with a modified Von Karman nose. Various canard surfaces for pitch control only were te sted on the body with the 10 deg flare and on the body with both sets of fins. The results indicated that the addition of a flared afterbody or cruciform fins produced configurations which were longitudinally and directionally stable. The body with 5 deg fins should be capable of producing higher normal accelerations than the flared body. A l l of the canard surfaces were effective longitudinal controls which produced net positive increments of normal force and pitching moments which progressively decreased with increasing angle of attack

Improvement of a large-amplitude sinusoidal pressure generator for dynamic calibration of pressure transducers

Results of research on the improvement of a sinusoidal pressure generator are presented. The generator is an inlet-area-modulated, gas-flow-through device (siren type) which was developed to dynamically calibrate pressure transducers and pressure probes. Tests were performed over a frequency range of 100 Hz to 20 kHz at average chamber pressures (bias pressure) between 30 and 50 psia (21 and 35 N/sq cm abs) and between 150 and 300 psia (104 and 207 N/sq cm abs). Significant improvements in oscillation pressure waveform were obtained but with reduction in available generator oscillation pressure amplitude range. Oscillation pressure amplitude, waveform, and waveform spectral content are given as functions of frequency for the two bias pressure conditions. The generator and instrumentation for frequency, amplitude, and spectrum measurements are described