265 research outputs found
Post-war industrial expansion near the center of Boston
Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of City and Regional Planning, 1960.Includes bibliographical references (leaf 54).by E. Jack Schoop.M.C.P
Magneto-optical probe of the fully gapped Dirac band in ZrSiS
We present a far-infrared magneto-optical study of the gapped nodal-line
semimetal ZrSiS in magnetic fields up to 7 T. The observed field-dependent
features, which represent intra- (cyclotron resonance) and interband
transitions, develop as in increasing field and can be consistently
explained within a simple 2D Dirac band model with a gap of 26 meV and an
averaged Fermi velocity of m/s. This indicates a rather narrow
distribution of these parameters along the in-plane portions of the nodal line
in the Brillouin zone. A field-induced feature with an energy position that
does not depend on is also detected in the spectra. Possible origins of
this feature are discussed.Comment: accepted to Phys. Rev. Researc
Calcifediol is a safe and effective metabolite for raising vitamin D status and improving growth and feed conversion in rainbow trout
The vitamin D endocrine system is required for the transcriptional regulation of a myriad of vertebrate genes including those involved in bone health, growth, nutrient metabolism and immunity. The requirements of salmonids for vitamin D are amongst the highest for any aquaculture species. With nuances, the metabolism of the pre-vitamin cholecalciferol (D3) via calcifediol (25-OH-D3), required to produce the physiologically active hormone calcitriol (1,25-OH-D3) is conserved in fish. The composition of modern aquafeeds, growth in seawater and production challenges, such as disease, may result in the suboptimal biochemical activation of vitamin D hormone in fish.
A 91-day experimental feeding trial was used to test the safety and efficacy of calcifediol for the supply of vitamin D to rainbow trout with an initial body weight of 57.6 g. A practical diet containing cholecalciferol within recommended levels (5240 IU) was supplemented with either 69.8, 687 or 6854 μg/kg calcifediol. The efficacy of calcifediol was determined by the assessment of zootechnical performance and the appearance of vitamin D metabolites in the blood. The safety of the dietary interventions was assessed from generic health indices, examination of gross pathologies, hematology, and blood chemistry.
Test fish increased body weight at least 5.6-fold to 323.5 g over the experimental feeding period. The supplementation of 687 or 6854 μg/kg calcifediol resulted in significant improvements in growth rate and feed conversion (FCR). Whilst not detectable in control fish, calcifediol increased linearly according to dietary levels in the blood and to a lesser extent in the white muscle. The increases of calcifediol in the blood were accompanied by saturable increases of circulating active vitamin D. At the end of the 91-day feeding period, survival was 100%, no gross pathologies relating to the diets were observed, and health indices, hematology, and blood chemistry, including calcium and phosphorus, were not significantly altered.
The supplementation of calcifediol to practical diets containing recommended levels of cholecalciferol improves zootechnical performance and ensures that maximal levels of active vitamin D are present in the blood to meet physiological demands. With a lack of significant effects on health indices, hematology, and blood chemistry, including calcium and phosphorus, the tested high doses of calcifediol are concluded to be safe for salmonids
Field-induced quasi-particle tunneling in the nodal-line semimetal HfSiS revealed by de Haas-van Alphen quantum oscillations
We present a de Haas–van Alphen quantum oscillation study of the Dirac nodal-line semimetal HfSiS up to 32 T to unravel the structure of the high-frequency magnetic breakdown spectrum that was previously obscured in transport experiments. Despite a threefold enhanced gap between adjacent electron and hole pockets relative to the sister compound ZrSiS, a large number of large-area magnetic breakdown orbits enclosing the nodal-loop are identified. All breakdown orbits are assigned by extracting their cyclotron masses. Moreover, one additional low-frequency magnetic breakdown orbit, previously absent in ZrSiS, is observed and attributed to the larger spin-orbit interaction in HfSiS
Electron-Hole Tunneling Revealed by Quantum Oscillations in the Nodal-Line Semimetal HfSiS
We report a study of quantum oscillations in the high-field magnetoresistance of the nodal-line semimetal HfSiS. In the presence of a magnetic field up to 31 T parallel to the c axis, we observe quantum oscillations originating both from orbits of individual electron and hole pockets, and from magnetic breakdown between these pockets. In particular, we reveal a breakdown orbit enclosing one electron and one hole pocket in the form of a “figure of eight,” which is a manifestation of Klein tunneling in momentum space, although in a regime of partial transmission due to the finite separation between the pockets. The observed very strong dependence of the oscillation amplitude on the field angle and the cyclotron masses of the orbits are in agreement with the theoretical predictions for this novel tunneling phenomenon
Topological insulator in a Bi-BiSe infinitely adaptive superlattice phase
We report spin- and angle-resolved photoemission studies of a topological
insulator from the infinitely adaptive series between elemental Bi and
BiSe. The compound, based on BiSe, is a 1:1 natural
superlattice of alternating Bi layers and BiSe layers; the
inclusion of S allows the growth of large crystals, with the formula
BiSeS. The crystals cleave along the interfaces between the
Bi and BiSe layers, with the surfaces obtained having alternating
Bi or Se termination. The resulting terraces, observed by photoemission
electron microscopy, create avenues suitable for the study of one-dimensional
topological physics. The electronic structure, determined by spin- and angle-
resolved photoemission spectroscopy, shows the existence of a surface state
that forms a large, hexagonally shaped Fermi surface around the point
of the surface Brillouin zone, with the spin structure indicating that this
material is a topological insulator.Comment: published version, 5 pages, 4 figure
Modal Logics of Topological Relations
Logical formalisms for reasoning about relations between spatial regions play
a fundamental role in geographical information systems, spatial and constraint
databases, and spatial reasoning in AI. In analogy with Halpern and Shoham's
modal logic of time intervals based on the Allen relations, we introduce a
family of modal logics equipped with eight modal operators that are interpreted
by the Egenhofer-Franzosa (or RCC8) relations between regions in topological
spaces such as the real plane. We investigate the expressive power and
computational complexity of logics obtained in this way. It turns out that our
modal logics have the same expressive power as the two-variable fragment of
first-order logic, but are exponentially less succinct. The complexity ranges
from (undecidable and) recursively enumerable to highly undecidable, where the
recursively enumerable logics are obtained by considering substructures of
structures induced by topological spaces. As our undecidability results also
capture logics based on the real line, they improve upon undecidability results
for interval temporal logics by Halpern and Shoham. We also analyze modal
logics based on the five RCC5 relations, with similar results regarding the
expressive power, but weaker results regarding the complexity
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