21,804 research outputs found
Study of Growth in Recent and Fossil Invertebrate Exoskeletons and Its Relationship to Tidal Cycles in the Earth-moon System Semiannual Report, May 1 - Oct. 31, 1966
Growth cycles in fossil pelecypod shells and relationship to tidal cycles in earth-moon syste
Late Wenlock (middle Silurian) bio-events: Caused by volatile boloid impact/s
Late Wenlockian (late mid-Silurian) life is characterized by three significant changes or bioevents: sudden development of massive carbonate reefs after a long interval of limited reef growth; sudden mass mortality among colonial zooplankton, graptolites; and origination of land plants with vascular tissue (Cooksonia). Both marine bioevents are short in duration and occur essentially simultaneously at the end of the Wenlock without any recorded major climatic change from the general global warm climate. These three disparate biologic events may be linked to sudden environmental change that could have resulted from sudden infusion of a massive amount of ammonia into the tropical ocean. Impact of a boloid or swarm of extraterrestrial bodies containing substantial quantities of a volatile (ammonia) component could provide such an infusion. Major carbonate precipitation (formation), as seen in the reefs as well as, to a more limited extent, in certain brachiopods, would be favored by increased pH resulting from addition of a massive quantity of ammonia into the upper ocean. Because of the buffer capacity of the ocean and dilution effects, the pH would have returned soon to equilibrium. Major proliferation of massive reefs ceased at the same time. Addition of ammonia as fertilizer to terrestrial environments in the tropics would have created optimum environmental conditions for development of land plants with vascular, nutrient-conductive tissue. Fertilization of terrestrial environments thus seemingly preceded development of vascular tissue by a short time interval. Although no direct evidence of impact of a volatile boloid may be found, the bioevent evidence is suggestive that such an impact in the oceans could have taken place. Indeed, in the case of an ammonia boloid, evidence, such as that of the Late Wenlockian bioevents may be the only available data for impact of such a boloid
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Sand Penetration By High-Speed Projectiles
Tungsten projectiles were shot into sand at velocities between 600 and 2200 m/s. Penetration was maximum at about 775 m/s. Below that velocity, projectiles were apparently stabilized by a fin set. Above that velocity, projectiles were broken by transverse loads. High-speed penetration resulted in comminution of sand particles, reducing their size by about 1000 times.Mechanical Engineerin
STUDIES ON ABLATION OF OBJECTS TRAVERSING AN ATMOSPHERE
Ablation-type thermal protection of objects traversing an atmosphere - earth and mar
Lower bounds for communication capacities of two-qudit unitary operations
We show that entangling capacities based on the Jamiolkowski isomorphism may
be used to place lower bounds on the communication capacities of arbitrary
bipartite unitaries. Therefore, for these definitions, the relations which have
been previously shown for two-qubit unitaries also hold for arbitrary
dimensions. These results are closely related to the theory of the
entanglement-assisted capacity of channels. We also present more general
methods for producing ensembles for communication from initial states for
entanglement creation.Comment: 9 pages, 2 figures, comments welcom
Sixth Amendment Sentencing After \u3ci\u3eHurst\u3c/i\u3e
The U.S. Supreme Court’s 2016 decision in Hurst v. Florida, which struck down Florida’s capital sentencing scheme, altered the Court’s Sixth Amendment sentencing doctrine. That doctrine has undergone several important changes since it was first recognized. At times the doctrine has expanded, invalidating sentencing practices across the country, and at times it has contracted, allowing restrictions on judicial sentencing discretion based on findings that are not submitted to a jury. Hurst represents another expansion of the doctrine. Although the precise scope of the decision is unclear, the most sensible reading of Hurst suggests that any finding required before a judge may impose a higher sentence must first be submitted to a jury and proven beyond a reasonable doubt. This reading invalidates several state capital sentencing systems and several noncapital systems, and it would require dramatic changes to federal sentencing as well
Collisions with ice-volatile objects: Geological implications
The collision of the Earth with extra-terrestrial ice-volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record. These bodies would be analogs of the ice satellites found for the Jovian planets and suspected for comets and certain low density bodies in the Asteroid belt. Five generic end-members are postulated: (1) water ice; (2) dry ice: carbon-carbon dioxide rich, (3) oceanic (chloride) ice; (4) sulfur-rich ice; (5) ammonia hydrate-rich ice; and (6) clathrate: methane-rich ice. Due to the volatile nature of these bodies, evidence for their impact with the Earth would be subtle and probably best reflected geochemically or in the fossil record. Actual boloids impacting the Earth may have a variable composition, generally some admixture with water ice. However for discussion purposes, only the effects of a dominant component will be treated. The general geological effects of such collisions, as a function of the dominant component would be: (1) rapid sea level rise unrelated to deglaciation, (2) decreased oceanic pH and rapid climatic warming or deglaciation; (3) increased paleosalinities; (4) increased acid rain; (5) increased oceanic pH and rapid carbonate deposition; and (6) rapid climatic warming or deglaciation
Relations for classical communication capacity and entanglement capability of two-qubit operations
Bipartite operations underpin both classical communication and entanglement
generation. Using a superposition of classical messages, we show that the
capacity of a two-qubit operation for error-free entanglement-assisted
bidirectional classical communication can not exceed twice the entanglement
capability. In addition we show that any bipartite two-qubit operation can
increase the communication that may be performed using an ensemble by twice the
entanglement capability.Comment: 4 page
Quantum dots in graphene
We suggest a way of confining quasiparticles by an external potential in a
small region of a graphene strip. Transversal electron motion plays a crucial
role in this confinement. Properties of thus obtained graphene quantum dots are
investigated theoretically for different types of the boundary conditions at
the edges of the strip. The (quasi)bound states exist in all systems
considered. At the same time, the dependence of the conductance on the gate
voltage carries an information about the shape of the edges.Comment: 4 pages, 3 figure
Constituency and origins of cyclic growth layers in pelecypod shells, part 1
Growth layers occurring in shells of 98 species of pelecypods were examined microscopically in thin section and as natural and etched surfaces. Study began with shells of eleven species known from life history investigations to have annual cycles of growth. Internal microstructural features of the annual layers in these shells provided criteria for recognition of similar, apparently annual shell increments in eighty-six of eighty-seven other species. All of the specimens feature growth laminae, commonly on the order of 50 microns in thickness. The specimens from shallow marine environments show either a clustering of growth laminae related to the formation of concentric ridges or minor growth bands on the external shell surface. Based on observations of the number of growth laminae and clusters per annual-growth layer, it was hypothesised that the subannual increments may be related to daily and fortnightly (and in some cases monthly) cycles in the environment. Possible applications of the paleogrowth method in the fields of paleoecology and paleoclimatology are discussed
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