1,345 research outputs found
Quantum buoyancy, generalized second law, and higher-dimensional entropy bounds
Bekenstein has presented evidence for the existence of a universal upper
bound of magnitude to the entropy-to-energy ratio of an
arbitrary {\it three} dimensional system of proper radius and negligible
self-gravity. In this paper we derive a generalized upper bound on the
entropy-to-energy ratio of a -dimensional system. We consider a box full
of entropy lowered towards and then dropped into a -dimensional black
hole in equilibrium with thermal radiation. In the canonical case of three
spatial dimensions, it was previously established that due to quantum buoyancy
effects the box floats at some neutral point very close to the horizon. We find
here that the significance of quantum buoyancy increases dramatically with the
number of spatial dimensions. In particular, we find that the neutral
(floating) point of the box lies near the horizon only if its length is
large enough such that , where is the Compton length of the
body and for . A consequence is that quantum
buoyancy severely restricts our ability to deduce the universal entropy bound
from the generalized second law of thermodynamics in higher-dimensional
spacetimes with . Nevertheless, we find that the universal entropy bound
is always a sufficient condition for operation of the generalized second law in
this type of gedanken experiments.Comment: 6 page
Patterns of regional cerebellar atrophy in genetic frontotemporal dementia
BACKGROUND: Frontotemporal dementia (FTD) is a heterogeneous neurodegenerative disorder with a strong genetic component. The cerebellum has not traditionally been felt to be involved in FTD but recent research has suggested a potential role. METHODS: We investigated the volumetry of the cerebellum and its subregions in a cohort of 44 patients with genetic FTD (20 MAPT, 7 GRN, and 17 C9orf72 mutation carriers) compared with 18 cognitively normal controls. All groups were matched for age and gender. On volumetric T1-weighted magnetic resonance brain images we used an atlas propagation and label fusion strategy of the Diedrichsen cerebellar atlas to automatically extract subregions including the cerebellar lobules, the vermis and the deep nuclei. RESULTS: The global cerebellar volume was significantly smaller in C9orf72 carriers (mean (SD): 99989 (8939) mm(3)) compared with controls (108136 (7407) mm(3)). However, no significant differences were seen in the MAPT and GRN carriers compared with controls (104191 (6491) mm(3) and 107883 (6205) mm(3) respectively). Investigating the individual subregions, C9orf72 carriers had a significantly lower volume than controls in lobule VIIa-Crus I (15% smaller, p < 0.0005), whilst MAPT mutation carriers had a significantly lower vermal volume (10% smaller, p = 0.001) than controls. All cerebellar subregion volumes were preserved in GRN carriers compared with controls. CONCLUSION: There appears to be a differential pattern of cerebellar atrophy in the major genetic forms of FTD, being relatively spared in GRN, localized to the lobule VIIa-Crus I in the superior-posterior region of the cerebellum in C9orf72, the area connected via the thalamus to the prefrontal cortex and involved in cognitive function, and localized to the vermis in MAPT, the 'limbic cerebellum' involved in emotional processing
Basal forebrain atrophy in frontotemporal dementia
Background: The basal forebrain is a subcortical structure that plays an important role in learning, attention, and memory. Despite the known subcortical involvement in frontotemporal dementia (FTD), there is little research into the role of the basal forebrain in this disease. We aimed to investigate differences in basal forebrain volumes between clinical, genetic, and pathological diagnoses of FTD. /
Methods: 356 patients with FTD were recruited from the UCL Dementia Research Centre and matched on age and gender with 83 cognitively normal controls. All subjects had a T1-weighted MR scan suitable for analysis. Basal forebrain volumes were calculated using the Geodesic Information Flow (GIF) parcellation method and were compared between clinical (148 bvFTD, 82 svPPA, 103 nfvPPA, 14 PPA-NOS, 9 FTD-MND), genetic (24 MAPT, 15 GRN, 26 C9orf72) and pathological groups (28 tau, 3 FUS, 35 TDP-43) and controls. A subanalysis was also performed comparing pathological subgroups of tau (11 Pick's disease, 6 FTDP-17, 7 CBD, 4 PSP) and TDP-43 (12 type A, 2 type B, 21 type C). /
Results: All clinical subtypes of FTD showed significantly smaller volumes than controls (p†0.010, ANCOVA), with svPPA (10% volumetric difference) and bvFTD (9%) displaying the smallest volumes. Reduced basal forebrain volumes were also seen in MAPT mutations (18%, p<0.0005) and in individuals with pathologically confirmed FTDP-17 (17%), Pick's disease (12%), and TDP-43 type C (8%) (p<0.001). /
Conclusion: Involvement of the basal forebrain is a common feature in FTD, although the extent of volume reduction differs between clinical, genetic, and pathological diagnoses. Tauopathies, particularly those with MAPT mutations, had the smallest volumes. However, atrophy was also seen in those with TDP-43 type C pathology (most of whom have svPPA clinically). This suggests that the basal forebrain is vulnerable to multiple types of FTD-associated protein inclusions
The TMEM106B risk allele is associated with lower cortical volumes in a clinically diagnosed frontotemporal dementia cohort
Hippocampal subfield volumetry: differential pattern of atrophy in different forms of genetic frontotemporal dementia
BACKGROUND: Frontotemporal dementia (FTD) is a heterogeneous neurodegenerative disorder, with a strong genetic component. Previous research has shown that medial temporal lobe atrophy is a common feature of FTD. However, no study has so far investigated the differential vulnerability of the hippocampal subfields in FTD.
OBJECTIVES: We aimed to investigate hippocampal subfield volumes in genetic FTD.
METHODS: We in6/2/2018vestigated hippocampal subfield volumes in a cohort of 75 patients with genetic FTD (age: mean (standard deviation) 59.3 (7.7) years; disease duration: 5.1(3.4) years; 29 with MAPT, 28 with C9orf72, and 18 with GRN mutations) compared with 97 age-matched controls (age: 62.1 (11.1) years). We performed a segmentation of their volumetric T1-weighted MRI scans to extract hippocampal subfields volumes. Left and right volumes were summed and corrected for total intracranial volumes.
RESULTS: All three groups had smaller hippocampi than controls. The MAPT group had the most atrophic hippocampi, with the subfields showing the largest difference from controls being CA1-4 (24â27%, p < 0.0005). For C9orf72, the CA4, CA1, and dentate gyrus regions (8â11%, p < 0.0005), and for GRN the presubiculum and subiculum (10â14%, p < 0.0005) showed the largest differences from controls.
CONCLUSIONS: The hippocampus was affected in all mutation types but a different pattern of subfield involvement was found in the three genetic groups, consistent with differential cortical-subcortical network vulnerability
Web Service Discovery in a Semantically Extended UDDI Registry: the Case of FUSION
Service-oriented computing is being adopted at an unprecedented rate, making the effectiveness of automated service discovery an increasingly important challenge. UDDI has emerged as a de facto industry standard and fundamental building block within SOA infrastructures. Nevertheless, conventional UDDI registries lack means to provide unambiguous, semantically rich representations of Web service capabilities, and the logic inference power required for facilitating automated service discovery. To overcome this important limitation, a number of approaches have been proposed towards augmenting Web service discovery with semantics. This paper discusses the benefits of semantically extending Web service descriptions and UDDI registries, and presents an overview of the approach put forward in project FUSION, towards semantically-enhanced publication and discovery of services based on SAWSDL
The information paradox: conflicts and resolutions
Many relativists have been long convinced that black hole evaporation leads
to information loss or remnants. String theorists have however not been too
worried about the issue, largely due to a belief that the Hawking argument for
information loss is flawed in its details. A recently derived inequality shows
that the Hawking argument for black holes with horizon can in fact be made
rigorous. What happens instead is that in string theory black hole microstates
have no horizons. Thus the evolution of radiation quanta with E ~ kT is
modified by order unity at the horizon, and we resolve the information paradox.
We discuss how it is still possible for E >> kT objects to see an approximate
black hole like geometry. We also note some possible implications of this
physics for the early Universe.Comment: 26 pages, 8 figures, Latex; (Expanded version of) proceedings for
Lepton-Photon 201
A Comparative Study of Voxel and Surface Based Cortical Thickness Methods in Frontotemporal Dementia
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