Experience-dependent plasticity in cortical and cerebellar regions of early- and late-trained musicians

A body of current evidence suggests that there is a sensitive period for musical training: people who begin training before the age of seven show better performance on tests of musical skill, and also show differences in brain structure – especially in motor cortical and cerebellar regions – compared with those who start later. In two studies, we investigated distributed patterns of structural differences between early-trained (ET) and late-trained (LT) musicians. First, we examined structural covariation between cerebellar volume and cortical thickness (CT) in sensorimotor regions in ET and LT musicians and non-musicians (NMs). We found that early musical training had a specific effect on structural covariance between the cerebellum and cortex: NMs showed negative correlations between left lobule VI and right pre-supplementary motor area (preSMA) and premotor cortex (PMC), but this relationship was reduced in ET musicians. ETs instead showed a significant negative correlation between vermal IV and right pre-SMA and dPMC. In the second study, we used support vector machine models – a subtype of supervised machine learning – to investigate cortico-cerebellar structural covariation and to better understand the age boundaries of the sensitive period for early musicianship. Our model identified a combination of 17 regions, including 9 cerebellar and 8 sensorimotor regions, that accurately identified ET and LT musicians with high sensitivity and specificity. Critically, this model – which defined ET musicians as those who began their training before the age of 7 – outperformed all other models in which age of start was earlier or later (between ages 5-10). Our model’s ability to accurately classify ET and LT musicians provides additional evidence that musical training before age 7 affects cortico-cerebellar structure in adulthood, and is consistent with the hypothesis that connected brain regions interact during development to reciprocally influence brain and behavioural maturation. Together, these results suggest that early musical training has differential impacts on the maturation of cortico-cerebellar networks important for optimizing sensorimotor performance. This work enriches our understanding of how experience-dependent plasticity is affected by early musical training, providing a more nuanced understanding of the interrelated nature of brain development

Critical Behavior of the Marinari-Parisi Model

We consider the continuum string theory corresponding to the Marinari-Parisi supersymmetric matrix model. We argue that the world-sheet physics is exotic, and different from any known supersymmetric string theory. The embedding superspace coordinates become disordered on the world-sheet, but because of the noncompactness of the embedding time the disorder becomes complete only at asymptotic world-sheet scales.Comment: 7 pages, LaTe

Black Holes and Random Matrices

We argue that the late time behavior of horizon fluctuations in large anti-de Sitter (AdS) black holes is governed by the random matrix dynamics characteristic of quantum chaotic systems. Our main tool is the Sachdev-Ye-Kitaev (SYK) model, which we use as a simple model of a black hole. We use an analytically continued partition function $|Z(\beta +it)|^2$ as well as correlation functions as diagnostics. Using numerical techniques we establish random matrix behavior at late times. We determine the early time behavior exactly in a double scaling limit, giving us a plausible estimate for the crossover time to random matrix behavior. We use these ideas to formulate a conjecture about general large AdS black holes, like those dual to 4D super-Yang-Mills theory, giving a provisional estimate of the crossover time. We make some preliminary comments about challenges to understanding the late time dynamics from a bulk point of view.Comment: 73 pages, 15 figures, minor errors correcte

Measurement and Analysis of Ultrapeer-based P2P Search Networks

Unstructured Networks have been used extensively in P2P search systems today primarily for file sharing. These networks exploit heterogeneity in the network and offload most of the query processing load to more powerful nodes. As an alternative to unstructured networks, there have been recent proposals for using inverted indexes on structured networks for searching. These structured networks, otherwise known as distributed hash tables (DHTs), guarantee recall and are well suited for locating rare items. However, they may incur significant bandwidth for keyword-based searches. This paper performs a measurement study of Gnutella, a popular unstructured network used for file sharing. We focus primarily on studying Gnutella\u27s search performance and recall, especially in light of recent ultrapeer enhancements. Our study reveals significant query overheads in Gnutella ultrapeers, and the presence of queries that may benefit from the use of DHTs. Based on our study, we propose the use of a hybrid search infrastructure to improve the search coverage for rare items and present some preliminary performance results

Flows and Solitary Waves in Unitary Matrix Models with Logarithmic Potentials

We investigate unitary one-matrix models coupled to bosonic quarks. We derive a flow equation for the square-root of the specific heat as a function of the renormalized quark mass. We show numerically that the flows have a finite number of solitary waves, and we postulate that their number equals the number of quark flavors. We also study the nonperturbative behavior of this theory and show that as the number of flavors diverges, the flow does not reach two-dimensional gravity.Comment: 26 pages + 4 figure

Tetrahydrobiopterin Supplementation Improves Endothelial Function But Does Not Alter Aortic Stiffness in Patients With Rheumatoid Arthritis.

BACKGROUND: Rheumatoid arthritis is a systemic inflammatory condition associated with increased cardiovascular risk that may be due to underlying endothelial dysfunction and subsequent aortic stiffening. We hypothesized that supplementation with tetrahydrobiopterin (BH4) would recouple endothelial nitric oxide synthase and thus improve endothelial function and consequently reduce aortic stiffness. METHODS AND RESULTS: We conducted 2 randomized, double-blinded, placebo-controlled crossover studies examining 2 separate regimens: an acute regimen, with a single dose of BH4 400 mg versus placebo (n=18), and a short-term regimen, composed of a 1-week treatment with BH4 400 mg once daily versus placebo (n=15). Flow-mediated dilatation and aortic pulse wave velocity were studied 4 times, before and after each treatment phase. Acute BH4 supplementation led to an improvement of flow-mediated dilatation, whereas placebo had no effect (mean±SD of effect difference 2.56±4.79%; P=0.03). Similarly, 1-week treatment with BH4 improved endothelial function, but there was no change with placebo (mean±SD of effect difference 3.50±5.05%; P=0.02). There was no change in aortic pulse wave velocity following acute or short-term BH4 supplementation or placebo (mean±SD of effect difference: acute 0.09±0.67 m/s, P=0.6; short-term 0.03±1.46 m/s, P=0.9). CONCLUSION: Both acute and short-term supplementation with oral BH4 improved endothelial function but not aortic stiffness. This result suggests that BH4 supplementation may be beneficial for patients with rheumatoid arthritis by improving endothelial dysfunction and potentially reducing risk of cardiovascular disease. There appears to be no causal relationship between endothelial function and aortic stiffness, suggesting that they occur in parallel, although they may share common risk factors such as inflammation.KMMP and IBW were funded by British Heart Foundation. IBW, JC and NS received funding from the Comprehensive Local Research Network and IBW and JC from the National Institute for Health Research: Cambridge Biomedical Research Centre.This is the final version of the article. It first appeared from Wiley Blackwell via http://dx.doi.org/10.1161/JAHA.115.00276

Open Heterotic Strings

We classify potential cosmic strings according to the topological charge measurable outside the string core. We conjecture that in string theory it is this charge that governs the stability of long strings. This would imply that the SO(32) heterotic string can have endpoints, but not the E_8 x E_8 heterotic string. We give various arguments in support of this conclusion.Comment: 15 pages. v.2: typos, references correcte

Gravitational Scattering in the c = 1 Matrix Model

The $c=1$ matrix model is equivalent to $1+1$ dimensional string theory. However, the tachyon self-interaction in the former is local, while in the latter it is nonlocal due to the gravitational, dilaton and higher string fields. By studying scattering of classical pulses we show that the appropriate nonlocal field redefinition converts the local matrix model interaction into the expected string form. In particular, we see how the asymptotic behavior of the gravitational field appears in the scattering.Comment: 20 pages + 2 figures (included as a uufile), LaTe

Querying at Internet Scale

We are developing a distributed query processor called PIER, which is designed to run on the scale of the entire Internet. PIER utilizes a Distributed Hash Table (DHT) as its communication substrate in order to achieve scalability, reliability, decentralized control, and load balancing. PIER enhances DHTs with declarative and algebraic query interfaces, and underneath those interfaces implements multihop, in-network versions of joins, aggregation, recursion, and query/result dissemination. PIER is currently being used for diverse applications, including network monitoring, keyword-based filesharing search, and network topology mapping. We will demonstrate PIER\u27s functionality by showing system monitoring queries running on PlanetLab, a testbed of over 300 machines distributed across the globe

Dirichlet-Branes and Ramond-Ramond Charges

We show that Dirichlet-branes, extended objects defined by mixed Dirichlet-Neumann boundary conditions in string theory, break half of the supersymmetries of the type~II superstring and carry a complete set of electric and magnetic Ramond-Ramond charges. We also find that the product of the electric and magnetic charges is a single Dirac unit, and that the quantum of charge takes the value required by string duality. This is strong evidence that the Dirchlet-branes are intrinsic to type II string theory and are the Ramond-Ramond sources required by string duality. We also note the existence of a previously overlooked 9-form potential in the IIa string, which gives rise to an effective cosmological constant of undetermined magnitude.Comment: LaTeX, 10 pages. Minor typos corrected in eq. 8, 9, 13. References added to [11