19,986 research outputs found
Should the United States hold foreign currency reserves?
An argument that for countries with well-developed money markets and flexible exchange rates, there is little to be gained from holding a vast foreign exchange portfolio and intervening in the world's currency markets.Foreign exchange - Law and legislation
Thermal constraints on in vivo optogenetic manipulations.
A key assumption of optogenetics is that light only affects opsin-expressing neurons. However, illumination invariably heats tissue, and many physiological processes are temperature-sensitive. Commonly used illumination protocols increased the temperature by 0.2-2 °C and suppressed spiking in multiple brain regions. In the striatum, light delivery activated an inwardly rectifying potassium conductance and biased rotational behavior. Thus, careful consideration of light-delivery parameters is required, as even modest intracranial heating can confound interpretation of optogenetic experiments
Symmetrical and asymmetrical separations about a yawed cone
Three dimensional flow separations about a circular cone were investigated in the Mach number range 0.6 - 1.8. The cone was tested in the Ames 1.8 by 1.8 m wind tunnel at Reynolds numbers based on the cone length from 4,500,000 to 13,500,000 under nominally zero heat transfer conditions. Results indicate that: (1) the lee-side separated flow develops from initially symmetrically disposed and near-conical separation lines at angle of incidence/cone semiangle equal to approximately 1, with the free shear layers eventually rolling up into tightly coiled vortices at all Mach numbers; (2) the onset of asymmetry of the lee-side separated flow about the mean pitch plane is sensitive to Mach number, Reynolds number, and the nose bluntness; and (3) as the Mach number is increased beyond 1.8, the critical angle of incidence for the onset of asymmetry increases until at about M = 2.75 there is no longer any significant side force development
Radio and X-ray properties of submillimeter galaxies in the A2125 field
We present the radio and X-ray properties of 1.2 mm MAMBO source candidates
in a 1600 sq. arcmin field centered on the Abell 2125 galaxy cluster at
z=0.247. The brightest, non-synchrotron mm source candidate in the field has a
photometric redshift, z = 3.93^+1.11_-0.80, and is not detected in a 31 ks
Chandra X-ray exposure. These findings are consistent with this object being an
extremely dusty and luminous starburst galaxy at high-redshift, possibly the
most luminous yet identified in any blank-field mm survey. The deep 1.4 GHz VLA
imaging identifies counterparts for 83% of the 29 mm source candidates
identified at >=4-sigma S(1.2mm) = 2.7 - 52.1 mJy, implying that the majority
of these objects are likely to lie at z <~ 3.5. The median mm-to-radio
wavelength photometric redshift of this radio-detected sample is z~2.2 (first
and third quartiles of 1.7 and 3.0), consistent with the median redshift
derived from optical spectroscopic surveys of the radio-detected subsample of
bright submm galaxies (S(850um) > 5 mJy). Three mm-selected quasars are
confirmed to be X-ray luminous in the high resolution Chandra imaging, while
another mm source candidate with potential multiple radio counterparts is also
detected in the X-ray regime. Both of these radio counterparts are positionally
consistent with the mm source candidate. One counterpart is associated with an
elliptical galaxy at z = 0.2425, but we believe that a second counterpart
associated with a fainter optical source likely gives rise to the mm emission
at z~1.Comment: Accepted for publication in Ap
Endotaxial Si nanolines in Si(001):H
We present a detailed study of the structural and electronic properties of a
self-assembled silicon nanoline embedded in the H-terminated silicon (001)
surface, known as the Haiku stripe. The nanoline is a perfectly straight and
defect free endotaxial structure of huge aspect ratio; it can grow micrometre
long at a constant width of exactly four Si dimers (1.54nm). Another remarkable
property is its capacity to be exposed to air without suffering any
degradation. The nanoline grows independently of any step edges at tunable
densities, from isolated nanolines to a dense array of nanolines. In addition
to these unique structural characteristics, scanning tunnelling microscopy and
density functional theory reveal a one-dimensional state confined along the
Haiku core. This nanoline is a promising candidate for the long sought after
electronic solid-state one-dimensional model system to explore the fascinating
quantum properties emerging in such reduced dimensionality.Comment: 8 pages, 6 figure
Low voltage control of ferromagnetism in a semiconductor p-n junction
The concept of low-voltage depletion and accumulation of electron charge in
semiconductors, utilized in field-effect transistors (FETs), is one of the
cornerstones of current information processing technologies. Spintronics which
is based on manipulating the collective state of electron spins in a
ferromagnet provides complementary technologies for reading magnetic bits or
for the solid-state memories. The integration of these two distinct areas of
microelectronics in one physical element, with a potentially major impact on
the power consumption and scalability of future devices, requires to find
efficient means for controlling magnetization electrically. Current induced
magnetization switching phenomena represent a promising step towards this goal,
however, they relay on relatively large current densities. The direct approach
of controlling the magnetization by low-voltage charge depletion effects is
seemingly unfeasible as the two worlds of semiconductors and metal ferromagnets
are separated by many orders of magnitude in their typical carrier
concentrations. Here we demonstrate that this concept is viable by reporting
persistent magnetization switchings induced by short electrical pulses of a few
volts in an all-semiconductor, ferromagnetic p-n junction.Comment: 11 pages, 4 figure
A Comprehensive Radio and Optical Study of Abell 2256: Activity from an Infalling Group
Abell 2256 is a nearby (z~0.06), rich cluster of galaxies with fascinating
observed properties across a range of wavelengths. Long believed to represent a
cluster merger, recent X-ray and optical results have suggested that in
addition to the primary cluster and subcluster there is evidence for a third,
poorer system. We present wide-field, high sensitivity 1.4 GHz VLA radio
observations of Abell 2256 in conjunction with optical imaging and additional
spectroscopy. Over 40 cluster radio galaxies are identified, with optical
spectroscopy indicating the emission source (star formation or AGN) for most of
them. While the overall fraction of galaxies exhibiting radio emission is
consistent with a large sample of other nearby clusters, we find an increase in
the activity level of galaxies belonging to the third system (hereafter, the
``Group''). Specifically, the Group has relatively more star formation than
both the primary cluster and main subcluster. The position of the Group is also
coincident with the observed cluster radio relic. We suggest that the Group
recently (~0.3 Gyr) merged with the primary cluster and that this merger, not
the ongoing merger of the primary and the main subcluster, might be responsible
for many of the unusual radio properties of Abell 2256. Furthermore, the
greater star formation activity of the Group suggests that the infall of groups
is an important driver of galaxy evolution in clusters.Comment: 21 pages plus 13 JPEG figures; to appear in the Astronomical Journa
One dimensional Si-in-Si(001) template for single-atom wire growth
Single atom metallic wires of arbitrary length are of immense technological
and scientific interest. We describe a novel silicon-only template enabling the
self-organised growth of isolated micrometer long surface and subsurface
single-atom chains. It consists of a one dimensional, defect-free
reconstruction - the Haiku core, here revealed for the first time in details -
self-assembled on hydrogenated Si(001) terraces, independent of any step edges.
We discuss the potential of this Si-in-Si template as an appealing alternative
to vicinal surfaces for nanoscale patterning.Comment: 3 pages, 2 figure
Comparison of the anabolic effects of reported osteogenic compounds on human mesenchymal progenitor-derived osteoblasts
There is variability in the reported effects of compounds on osteoblasts arising from differences in experimental design and choice of cell type/origin. This makes it difficult to discern a compound’s action outside its original study and compare efficacy between compounds. Here, we investigated five compounds frequently reported as anabolic for osteoblasts (17β-estradiol (oestrogen), icariin, lactoferrin, lithium chloride, and menaquinone-4 (MK-4)) on human mesenchymal progenitors to assess their potential for bone tissue engineering with the aim of identifying a potential alternative to expensive recombinant growth factors such as bone morphogenetic protein 2 (BMP-2). Experiments were performed using the same culture conditions to allow direct comparison. The concentrations of compounds spanned two orders of magnitude to encompass the reported efficacious range and were applied continuously for 22 days. The effects on the proliferation (resazurin reduction and DNA quantification), osteogenic differentiation (alkaline phosphatase (ALP) activity), and mineralised matrix deposition (calcium and collagen quantification) were assessed. Of these compounds, only 10 µM MK-4 stimulated a significant anabolic response with 50% greater calcium deposition. Oestrogen and icariin had no significant effects, with the exception of 1 µM icariin, which increased the metabolic activity on days 8 and 22. 1000 µg/mL of lactoferrin and 10 mM lithium chloride both significantly reduced the mineralised matrix deposition in comparison to the vehicle control, despite the ALP activity being higher in lithium chloride-treated cells at day 15. This demonstrates that MK-4 is the most powerful stimulant of bone formation in hES-MPs of the compounds investigated, highlighting its potential in bone tissue engineering as a method of promoting bone formation, as well as its prospective use as an osteoporosis treatment
Reptiles of Rancho Grande and vicinity, Estado Aragua, Venezuela
http://deepblue.lib.umich.edu/bitstream/2027.42/56372/1/MP128.pd
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