1,317 research outputs found
Self-Assembly in the Growth of Precious Opal
It is proposed that primary nucleation of amorphous microspherulites of
hydrated silica in natural proto-precious-opal can be followed by a long range
superlattice ordering process by means of electrostatic self-assembly.
Necessary conditions in the thermodynamics are a high surface charge density on
microspherulite surfaces, a long Debye length and an appropriate number density
of nucleation centres. A further chemical requirement is a high alkaline
environmental pH from 9 to 10. It is also proposed that the characteristic
concentric spherical shell-like structure of spherulites, centred on primary
nuclei, are due to sequential deposition of intrinsic salts which precipitate
out when the corresponding solubility limits in the liquid are successively
exceeded. It can be that the better-known sedimentation of microspherulites
under gravity only plays part in the final stabilization period of overall
growth.Comment: 12 pages pdf http://dx.doi.org/10.1016/j.jcrysgro.2009.09.04
Crustal Accretion in the Gulf of California: An Intermediaterate Spreading Axis
An important objective of Deep Sea Drilling Project
(DSDP) Leg 65 was to study crustal accretion at an ocean
ridge axis with an intermediate-spreading rate for comparison
with previously studied sections displaying slowand
fast-spreading rates. The southern Gulf of California
was selected for this purpose because the basement displays
high seismic velocities (comparable to those observed
for Cretaceous basement in the western North
Atlantic) and high ambient sedimentation rates, which
facilitated penetration of zero-age basement. Four sites
were drilled, forming an axial transect immediately south
of the Tamayo Fracture Zone (Figs. 1 and 2) and providing
a series of characteristic sections into the crust. This
chapter attempts to provide a brief synthesis of the results
from Leg 65, focusing particularly on the lithology,
geochemistry, and paleomagnetic properties of the
cored basement material. From these data, we present
an interpretation of the processes of magmatic evolution
and crustal accretion occurring at the Gulf of California
spreading axis
Some recent radio talks.
Myxomatosis is losing its punch - By A. R. TOMLINSON, Chief Vermin Control Officer
The results of the testing of field strains of myxomatosis just released by the Australian National University are of vital importance to every farmer in Western Australia. They show clearly that the predicted decline in the effectiveness of myxomatosis has occurred. Worse still, they reveal that the decline has been more rapid in some areas than observers anticipated.
The importance of good seed in vegetable production. - By T. WACHTEL, Vegetable Adviser, Horticultural Division
The seed is the foundation of the crop that eventually is to be harvested. As an American textbook on vegetable vegetable growing puts it: Within the seed coat may be locked up the key to future success or failure. A vegetable crop can be much poorer than the seed, but it cannot be better.
Water conservation on the farm - By J. W. LEWIS, Irrigation Adviser, Bunbury
Water conservation on the farm is becoming increasingly important in this State, and on most properties in the South-West water can be conserved easily and economically. Coupled with the use of modern spray irrigation systems, this trend may well revolutionise farming methods in years to come and lead the way to greater agricultural prosperity.
Itch mite in sheep - By C. R. TOOP, Chief Veterinary Surgeon
During the past 12 months there has been a sharp rise in the incidence of itch mite and many cases have been reported both from sheep markets and individual properties. The symptoms of itch mite infestation are very similar to those produced by hce but, unlike the sheep louse, the itch mite is invisible to the naked eye and the microscopic examination of scrapings taken from the skin after the wool has been closely clipped is necessary for its detection.
Orchard irrigation - By J. CRIPPS, Horticultural Adviser
There are no fruits grown in Western Australia which do not give larger crops if irrigated, although the majority of fruit growers do not have irrigation installations.
Powdery mildew diseases in the home garden - By OLGA M. GOSS, B.Sc. Hons., Plant Pathologist
Most of you will be only too familiar with the powdery mildew diseases which occur so frequently during the warmer months in your gardens. The most common plants badly affected by these diseases are grape vines, roses, hydrangeas, delphinium, Iagerstroemia and melons of various types.
Cat Flu - A matter of serious concern - By J. SHILKIN, B.V.Sc, Veterinary Surgeon
The importance of cats in the community is not generally realised by the public, yet severe epidemics among the feline population should be a matter of considerable concern. The presence of a reasonably large cat population in our cities is most important in keeping rat and mice numbers down to a low level, and their importance on farming properties is too well known to need any comment. Rat-borne diseases do occur m man in Australia and rats are always a potential danger as carriers and spreaders of some extremely serious diseases of man.
Even good farmers can cause erosion. - By BRIAN MARSH, B.Sc. (Agric), Soil Conservation Adviser
The particular aspects of soil conservation I am to discuss has not been publicised before, and the suggestions contained in this talk may be of use to you during seeding operations this year. It is often asked, Will the use of clover really prevent erosion
mTORC2 signaling drives the development and progression of pancreatic cancer
mTOR signaling controls several critical cellular functions and is deregulated in many cancers, including pancreatic cancer. To date, most efforts have focused on inhibiting the mTORC1 complex. However, clinical trials of mTORC1 inhibitors in pancreatic cancer have failed, raising questions about this therapeutic approach. We employed a genetic approach to delete the obligate mTORC2 subunit Rictor and identified the critical times during which tumorigenesis requires mTORC2 signaling. Rictor deletion resulted in profoundly delayed tumorigenesis. Whereas previous studies showed most pancreatic tumors were insensitive to rapamycin, treatment with a dual mTORC1/2 inhibitor strongly suppressed tumorigenesis. In late-stage tumor-bearing mice, combined mTORC1/2 and PI3K inhibition significantly increased survival. Thus, targeting mTOR may be a potential therapeutic strategy in pancreatic cancer
Minimally Invasive Mitral Valve Surgery I: Patient Selection, Evaluation, and Planning.
Widespread adoption of minimally invasive mitral valve repair and replacement may be fostered by practice consensus and standardization. This expert opinion, first of a 3-part series, outlines current best practices in patient evaluation and selection for minimally invasive mitral valve procedures, and discusses preoperative planning for cannulation and myocardial protection
Minimally Invasive Mitral Valve Surgery II: Surgical Technique and Postoperative Management.
Techniques for minimally invasive mitral valve repair and replacement continue to evolve. This expert opinion, the second of a 3-part series, outlines current best practices for nonrobotic, minimally invasive mitral valve procedures, and for postoperative care after minimally invasive mitral valve surgery
Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402
We report the results of long observing campaigns on two novalike variables:
V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra,
complex line profiles signifying mass loss at particular orbital phases, and
similar orbital periods (respectively 0.12433 and 0.12056 d). They are
well-credentialed members of the SW Sex class of cataclysmic variables. Their
light curves are also quite complex. V442 Oph shows periodic signals with
periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar
signals at 0.11696(8) d and 4.05(12) d. We interpret these short and long
periods respectively as a "negative superhump" and the wobble period of the
accretion disk. The superhump could then possibly arise from the heating of the
secondary (and structures fixed in the orbital frame) by inner-disk radiation,
which reaches the secondary relatively unimpeded since the disk is not
coplanar.
At higher frequencies, both stars show another type of variability:
quasi-periodic oscillations (QPOs) with a period near 1000 seconds. Underlying
these strong signals of low stability may be weak signals of higher stability.
Similar QPOs, and negative superhumps, are quite common features in SW Sex
stars. Both can in principle be explained by ascribing strong magnetism to the
white dwarf member of the binary; and we suggest that SW Sex stars are
borderline AM Herculis binaries, usually drowned by a high accretion rate. This
would provide an ancestor channel for AM Hers, whose origin is still
mysterious.Comment: PDF, 41 pages, 4 tables, 16 figures; accepted, in press, to appear
December 2002, PASP; more info at http://cba.phys.columbia.edu
Optical spectroscopy and photometry of SAX J1808.4−3658 in outburst
We present phase resolved optical spectroscopy and photometry of V4580 Sagittarii, the optical counterpart to the accretion powered millisecond pulsar SAX J1808.4−3658, obtained during the 2008 September/October outburst. Doppler tomography of the N iiiΛ4640.64 Bowen blend emission line reveals a focused spot of emission at a location consistent with the secondary star. The velocity of this emission occurs at 324 ± 15 km s −1 ; applying a ‘ K -correction’, we find the velocity of the secondary star projected on to the line of sight to be 370 ± 40 km s −1 . Based on existing pulse timing measurements, this constrains the mass ratio of the system to be 0.044 +0.005 −0.004 , and the mass function for the pulsar to be 0.44 +0.16 −0.13  M ⊙ . Combining this mass function with various inclination estimates from other authors, we find no evidence to suggest that the neutron star in SAX J1808.4−3658 is more massive than the canonical value of 1.4 M ⊙ . Our optical light curves exhibit a possible superhump modulation, expected for a system with such a low mass ratio. The equivalent width of the Ca ii H and K interstellar absorption lines suggest that the distance to the source is ∼2.5 kpc. This is consistent with previous distance estimates based on type-I X-ray bursts which assume cosmic abundances of hydrogen, but lower than more recent estimates which assume helium-rich bursts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74893/1/j.1365-2966.2009.14562.x.pd
Minimally Invasive Mitral Valve Surgery III: Training and Robotic-Assisted Approaches.
Minimally invasive mitral valve operations are increasingly common in the United States, but robotic-assisted approaches have not been widely adopted for a variety of reasons. This expert opinion reviews the state of the art and defines best practices, training, and techniques for developing a successful robotics program
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