4,191 research outputs found
Friction, Free Axes of Rotation and Entropy
Friction forces acting on rotators may promote their alignment and therefore
eliminate degrees of freedom in their movement. The alignment of rotators by
friction force was demonstrated by experiments performed with different
spinners, demonstrating how friction generates negentropy in a system of
rotators. A gas of rigid rotators influenced by friction force is considered.
The orientational negentropy generated by a friction force was estimated with
the Sackur-Tetrode equation. The minimal change in total entropy of a system of
rotators, corresponding to their eventual alignment, decreases with
temperature. The reported effect may be of the primary importance for a phase
equilibrium and motion of ubiquitous colloidal and granular systems.Comment: 10 pages, 7 image
Self-assembled levitating clusters of water droplets: pattern-formation and stability
Water forms ordered hexagonally symmetric structures (snow crystals) in its solid state, however not as liquid. Typically, mists and clouds are composed of randomly moving small droplets lacking any ordered structure. Self-organized hexagonally patterned microdroplet clusters over locally heated water surfaces have been recently observed. However, many aspects of the phenomenon are far from being well understood including what determines droplets size, arrangement, and the distance between them. Here we show that the Voronoi entropy of the cluster tends to decrease indicating to their selforganization, while coupling of thermal effects and mechanical forces controls the stability of the clusters. We explain the balance of the long-range attraction and repulsion forces which stabilizes the cluster patterns and established the range of parameters, for which the clusters are stable. The cluster is a dissipative structure similar to self-organized RayleighâBĂ©nard convective cells. Microdroplet formation plays a role in a variety effects from mist and clouds to aerosols. We anticipate that the discovery of the droplet cluster phenomenon and its explanation will provide new insights on the fundamental physical and chemical processes such as microdroplet role in reaction catalysis in nature as well as new tools for aerosol analysis and microfluidic applications
Directing self-assembly to grow adaptive physical structures
Additive manufacturing technologies offer exciting opportunities to rethink the process of designing and fabricating physical structures. This paper outlines initial work that seeks to extend existing AM capabilities, creating physically adaptive structures by exploiting processes of self-assembling materials. The paper details an investigation of self-assembling structures that can respond to different conditions by adapting their physical properties over time. The process uses electrolysis of seawater to demonstrate a proof-of concept of tuneable material structures, via crystal growth. Results demonstrate an aggregation-based multi-material system that is sensitive to changing environmental conditions. Material properties of grown structures have been analysed and illustrate that different materials can be created from an abundant base material (seawater) by manipulating environmental conditions (i.e. electrical current). It is found that turbulence is a useful property within these kinds of systems and that the physical properties of cathode scaffold structures have a significant impact in controlling material properties and resolution
Numerically Stable Sparse Gaussian Processes via Minimum Separation using Cover Trees
Gaussian processes are frequently deployed as part of larger machine learning
and decision-making systems, for instance in geospatial modeling, Bayesian
optimization, or in latent Gaussian models. Within a system, the Gaussian
process model needs to perform in a stable and reliable manner to ensure it
interacts correctly with other parts of the system. In this work, we study the
numerical stability of scalable sparse approximations based on inducing points.
To do so, we first review numerical stability, and illustrate typical
situations in which Gaussian process models can be unstable. Building on
stability theory originally developed in the interpolation literature, we
derive sufficient and in certain cases necessary conditions on the inducing
points for the computations performed to be numerically stable. For
low-dimensional tasks such as geospatial modeling, we propose an automated
method for computing inducing points satisfying these conditions. This is done
via a modification of the cover tree data structure, which is of independent
interest. We additionally propose an alternative sparse approximation for
regression with a Gaussian likelihood which trades off a small amount of
performance to further improve stability. We provide illustrative examples
showing the relationship between stability of calculations and predictive
performance of inducing point methods on spatial tasks
Connectivity alterations of mesostriatal pathways in first episode psychosis
Background and hypothesisPathogenic understanding of the psychotic disorders converges on regulation of dopaminergic signaling in mesostriatocortical pathways. Functional connectivity of the mesostriatal pathways may inform us of the neuronal networks involved.Study designThis longitudinal study of first episode psychosis (FEP) (49 patients, 43 controls) employed seed-based functional connectivity analyses of fMRI data collected during a naturalistic movie stimulus.Study resultsWe identified hypoconnectivity of the dorsal striatum with the midbrain, associated with antipsychotic medication dose in FEP, in comparison with the healthy control group. The midbrain regions that showed hypoconnectivity with the dorsal striatum also showed hypoconnectivity with cerebellar regions suggested to be involved in regulation of the mesostriatocortical dopaminergic pathways. None of the baseline hypoconnectivity detected was seen at follow-up.ConclusionsThese findings extend earlier resting state findings on mesostriatal connectivity in psychotic disorders and highlight the potential for cerebellar regulation of the mesostriatocortical pathways as a target of treatment trials.Peer reviewe
Influence of the Fermi Surface Morphology on the Magnetic Field-Driven Vortex Lattice Structure Transitions in YBaCuO0, 0.15
We report small-angle neutron scattering measurements of the vortex lattice
(VL) structure in single crystals of the lightly underdoped cuprate
superconductor YBa2Cu3O6.85. At 2 K, and for fields of up to 16 T applied
parallel to the crystal c-axis, we observe a sequence of field-driven and
first-order transitions between different VL structures. By rotating the field
away from the c-axis, we observe each structure transition to shift to either
higher or lower field dependent on whether the field is rotated towards the
[100] or [010] direction. We use this latter observation to argue that the
Fermi surface morphology must play a key role in the mechanisms that drive the
VL structure transitions. Furthermore, we show this interpretation is
compatible with analogous results obtained previously on lightly overdoped
YBa2Cu3O7. In that material, it has long-been suggested that the high field VL
structure transition is driven by the nodal gap anisotropy. In contrast, the
results and discussion presented here bring into question the role, if any, of
a nodal gap anisotropy on the VL structure transitions in both YBa2Cu3O6.85 and
YBa2Cu3O7
Initial active surveillance for patients with metastatic renal cell carcinoma: 10âyears' experience at a regional cancer Centre
Abstract A subset of patients with metastatic renal cell carcinoma (mRCC) follow an indolent disease course and may benefit from initial active surveillance (AS). However, selecting patients suitable for this approach is challenging. To investigate this we sought to define outcomes of patients with mRCC suitable for initial AS. All patients with mRCC clinically selected for initial AS at the Edinburgh Cancer Centre between January 2010 and December 2020 were identified. Key inflammatory biomarkers (haemoglobin, white cell count, neutrophil count, platelets, Câreactive protein [CRP], albumin, corrected calcium) and the International Metastatic RCC Database Consortium (IMDC) risk score were measured. The relationship between these and time to systemic anticancer therapy (tSACT) and overall survival (OS) was analysed. Data were available for 160 patients. Estimated median overall survival was 88.0 (interquartile range [IQR] 34.0â127.0) months. Median tSACT was 31.8 (IQR 12.0â76.3) months. On multivariate analysis, only CRP was predictive of tSACT (HR 2.47 [95% CI:1.59â3.85] p â10 mg/L were more likely to commence SACT within 1 year than those with CRPâ€10 mg/L (41% vs. 18%, Relative Risk 2.16 (95% CI:1.18â3.96) (p =â0.012)). IMDC risk score was not predictive of tSACT or OS. Active surveillance is an appropriate initial management option for selected patients with mRCC. CRP, a biomarker of systemic inflammation, may provide additional objective information to assist clinical decisionâmaking in patients with mRCC being considered for initial AS. Although this is a retrospective observational study, the cohort is well defined and includes all patients managed with initial AS in an inclusive realâworld setting
BLAST: the Redshift Survey
The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has recently
surveyed ~8.7 deg^2 centered on GOODS-South at 250, 350, and 500 microns. In
Dye et al. (2009) we presented the catalogue of sources detected at 5-sigma in
at least one band in this field and the probable counterparts to these sources
in other wavebands. In this paper, we present the results of a redshift survey
in which we succeeded in measuring redshifts for 82 of these counterparts. The
spectra show that the BLAST counterparts are mostly star-forming galaxies but
not extreme ones when compared to those found in the Sloan Digital Sky Survey.
Roughly one quarter of the BLAST counterparts contain an active nucleus. We
have used the spectroscopic redshifts to carry out a test of the ability of
photometric redshift methods to estimate the redshifts of dusty galaxies,
showing that the standard methods work well even when a galaxy contains a large
amount of dust. We have also investigated the cases where there are two
possible counterparts to the BLAST source, finding that in at least half of
these there is evidence that the two galaxies are physically associated, either
because they are interacting or because they are in the same large-scale
structure. Finally, we have made the first direct measurements of the
luminosity function in the three BLAST bands. We find strong evolution out to
z=1, in the sense that there is a large increase in the space-density of the
most luminous galaxies. We have also investigated the evolution of the
dust-mass function, finding similar strong evolution in the space-density of
the galaxies with the largest dust masses, showing that the luminosity
evolution seen in many wavebands is associated with an increase in the
reservoir of interstellar matter in galaxies.Comment: Accepted for publication in the Astrophysical Journal. Maps and
associated results are available at http://blastexperiment.info
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Climate Change during and after the Roman Empire: Reconstructing the Past from Scientific and Historical Evidence
Growing scientific evidence from modern climate science is loaded with implications for the environmental history of the Roman Empire and its successor societies. The written and archaeological evidence, although richer than commonly realized, is unevenly distributed over time and space. A first synthesis of what the written records and multiple natural archives (multi-proxy data) indicate about climate change and variability across western Eurasia from c. 100 b.c. to 800 a.d. confirms that the Roman Empire rose during a period of stable and favorable climatic conditions, which deteriorated during the Empire's third-century crisis. A second, briefer period of favorable conditions coincided with the Empire's recovery in the fourth century; regional differences in climate conditions parallel the diverging fates of the eastern and western Empires in subsequent centuries. Climate conditions beyond the Empire's boundaries also played an important role by affecting food production in the Nile valley, and by encouraging two major migrations and invasions of pastoral peoples from Central Asia.Earth and Planetary SciencesHistor
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