14,557 research outputs found
Charles W. Peach, palaeobotany and Scotland
The move south from Wick to the city of Edinburgh in 1865, some four years after retirement from the Customs service, provided Charles W. Peach with new opportunities for fossil-collecting and scientific networking. Here he renewed and maintained his interest in natural history and made significant palaeobotanical collections from the Carboniferous of the Midland Valley of Scotland. These are distinguished by some interesting characteristics of their documentation which the following generations of fossil collectors and researchers would have done well to emulate. Many of his fossil plant specimens have not only the locality detail,but also the date, month and year of collection neatly handwritten on attached paper labels; as a result, we can follow Peach's collecting activities over a period of some 18 years or so. Comments and even illustrative sketches on the labels of some fossils give us first-hand insight into Peach's observations. Study of these collections now held in National Museums Scotland reveals a pattern of collecting heavily biased towards those localities readily accessible from the newly expanding railways which provided a relatively inexpensive and convenient means of exploring the geology of the neighbourhood of Edinburgh.
Charles W. Peach had a very 'hands-on' practical approach to scientific investigation which led him to construct novel glass plates with mounted Sphenopteris cuticle, removed intact from Lower Carboniferous shales and limestones originating in West Lothian. These resemble the herbarium sheets with which he was familiar from his parallel and highly significant work on extant flora including nearshore marine algae. He also prepared hand ground glass microscope slides,particularly of permineralised plant material from Pettycur in Fife, using whatever materials he had to hand at the time. Peach's collection raises questions about the evolution of accepted standards of documentation in private collections, in parallel with the evolution of collecting practices by the new professionals such as the workers of the Geological Survey. Its relatively rapid deposition in museums,compared to many private collections, may also have contributed to its apparently high rate of usage by contemporary workers
High-Precision Thermodynamic and Critical Properties from Tensor Renormalization-Group Flows
The recently developed tensor renormalization-group (TRG) method provides a
highly precise technique for deriving thermodynamic and critical properties of
lattice Hamiltonians. The TRG is a local coarse-graining transformation, with
the elements of the tensor at each lattice site playing the part of the
interactions that undergo the renormalization-group flows. These tensor flows
are directly related to the phase diagram structure of the infinite system,
with each phase flowing to a distinct surface of fixed points. Fixed-point
analysis and summation along the flows give the critical exponents, as well as
thermodynamic functions along the entire temperature range. Thus, for the
ferromagnetic triangular lattice Ising model, the free energy is calculated to
better than 10^-5 along the entire temperature range. Unlike previous
position-space renormalization-group methods, the truncation (of the tensor
index range D) in this general method converges under straightforward and
systematic improvements. Our best results are easily obtained with D = 24,
corresponding to 4624-dimensional renormalization-group flows.Comment: 6 pages, 5 figure
Shape and symmetry determine two-dimensional melting transitions of hard regular polygons
The melting transition of two-dimensional (2D) systems is a fundamental
problem in condensed matter and statistical physics that has advanced
significantly through the application of computational resources and
algorithms. 2D systems present the opportunity for novel phases and phase
transition scenarios not observed in 3D systems, but these phases depend
sensitively on the system and thus predicting how any given 2D system will
behave remains a challenge. Here we report a comprehensive simulation study of
the phase behavior near the melting transition of all hard regular polygons
with vertices using massively parallel Monte Carlo simulations
of up to one million particles. By investigating this family of shapes, we show
that the melting transition depends upon both particle shape and symmetry
considerations, which together can predict which of three different melting
scenarios will occur for a given . We show that systems of polygons with as
few as seven edges behave like hard disks; they melt continuously from a solid
to a hexatic fluid and then undergo a first-order transition from the hexatic
phase to the fluid phase. We show that this behavior, which holds for all
, arises from weak entropic forces among the particles. Strong
directional entropic forces align polygons with fewer than seven edges and
impose local order in the fluid. These forces can enhance or suppress the
discontinuous character of the transition depending on whether the local order
in the fluid is compatible with the local order in the solid. As a result,
systems of triangles, squares, and hexagons exhibit a KTHNY-type continuous
transition between fluid and hexatic, tetratic, and hexatic phases,
respectively, and a continuous transition from the appropriate "x"-atic to the
solid. [abstract truncated due to arxiv length limitations]
Intercalated Rare-Earth Metals under Graphene on SiC
Intercalation of rare earth metals ( = Eu, Dy, and Gd) is achieved by
depositing the metal on graphene that is grown on silicon-carbide (SiC)
and by subsequent annealing at high temperatures to promote intercalation. STM
images of the films reveal that the graphene layer is defect free and that each
of the intercalated metals has a distinct nucleation pattern. Intercalated Eu
forms nano-clusters that are situated on the vertices of a Moir{\`e} pattern,
while Dy and Gd form randomly distributed nano-clusters. X-ray magnetic
circular dichroism (XMCD) measurements of intercalated films reveal the
magnetic properties of these 's nano-clusters. Furthermore, field
dependence and temperature dependence of the magnetic moments extracted from
the XMCD show paramagnetic-like behaviors with moments that are generally
smaller than those predicted by the Brillouin function. XMCD measurements of
-oxides compared with those of the intercalated 's under graphene after
exposure to air for months indicate that the graphene membranes protect these
intercalants against oxidation.Comment: 9 pages, 7 figure
Non-dopplerian cosmological redshift parameters in a model of graviton-dusty universe
Possible effects are considered which would be caused by a hypothetical
superstrong interaction of photons or massive bodies with single gravitons of
the graviton background. If full cosmological redshift magnitudes are caused by
the interaction, then the luminosity distance in a flat non-expanding universe
as a function of redshift is very similar to the specific function which fits
supernova cosmology data by Riess et al. From another side, in this case every
massive body, slowly moving relatively to the background, would experience a
constant acceleration, proportional to the Hubble constant, of the same order
as a small additional acceleration of Pioneer 10, 11.Comment: 5 pages. It was presented: at SIGRAV'2000 Congress, Italy (this
version); in Proc. of the Int. Symp. "FFP 4" (9-13 Dec 2000, Hyderabad,
India), Sidharth& Altaisky, Eds., Kluwer Academic/Plenum, 2001;in Proc. of
the 4th Edoardo Amaldi Conference on GW (Perth, W. Australia, 8-13 July 2001
Intercalated europium metal in epitaxial graphene on SiC
X-ray magnetic circular dichroism (XMCD) reveal the magnetic properties of
intercalated europium metal under graphene on SiC(0001). Intercalation of Eu
nano-clusters (average size 2.5 nm) between graphene and SiC substate are
formed by deposition of Eu on epitaxially grown graphene that is subsequently
annealed at various temperatures while keeping the integrity of the graphene
layer. Using sum-rules analysis of the XMCD of Eu M edges at
K, our samples show paramagnetic-like behavior with distinct anomaly at T
90 K which may be related to the N{\`e}el transition, T = 91 K,
of bulk metal Eu. We find no evidence of ferromagnetism due to EuO or
antiferromagnetism due to EuO indicating that the graphene layer
protects the intercalated metallic Eu against oxidation over months of exposure
to atmospheric environment.Comment: 6 pages, 5 figure
Search for a Standard Explanation of the Pioneer Anomaly
The data from Pioneer 10 and 11 shows an anomalous, constant, Doppler
frequency drift that can be interpreted as an acceleration directed towards the
Sun of a_P = (8.74 \pm 1.33) x 10^{-8} cm/s^2. Although one can consider a new
physical origin for the anomaly, one first must investigate the contributions
of the prime candidates, which are systematics generated on board. Here we
expand upon previous analyses of thermal systematics. We demonstrate that
thermal models put forth so far are not supported by the analyzed data.
Possible ways to further investigate the nature of the anomaly are proposed.Comment: Changes made for publicatio
EXIT OF MEAT SLAUGHTER PLANTS DURING IMPLEMENTATION OF THE PR/HACCP REGULATIONS
Implementation of the Pathogen Reduction and Hazard Analysis and Critical Control Points (PR/HACCP) regulations has occurred across all U.S. meat and poultry plants. A probit model is estimated to determine which factors have affected the probability of red meat slaughter plant exit during implementation of the regulations. While controlling for plant-level, company-level, regional-level, and supply conditions that may affect the probability of plant exit, smaller plants are found to exhibit a much greater probability of exit than larger plants. Other factors affecting plant exit include plant age, market share relative to the degree of market concentration, regional entry rates, and state-level wage rates.Agribusiness,
- …