An analytically solvable model of probabilistic network dynamics

We present a simple model of network dynamics that can be solved analytically for uniform networks. We obtain the dynamics of response of the system to perturbations. The analytical solution is an excellent approximation for random networks. A comparison with the scale-free network, though qualitatively similar, shows the effect of distinct topology.Comment: 4 pages, 1 figur

Spectral Analysis and the Dynamic Response of Complex Networks

The eigenvalues and eigenvectors of the connectivity matrix of complex networks contain information about its topology and its collective behavior. In particular, the spectral density $\rho(\lambda)$ of this matrix reveals important network characteristics: random networks follow Wigner's semicircular law whereas scale-free networks exhibit a triangular distribution. In this paper we show that the spectral density of hierarchical networks follow a very different pattern, which can be used as a fingerprint of modularity. Of particular importance is the value $\rho(0)$, related to the homeostatic response of the network: it is maximum for random and scale free networks but very small for hierarchical modular networks. It is also large for an actual biological protein-protein interaction network, demonstrating that the current leading model for such networks is not adequate.Comment: 4 pages 14 figure

Med Student Fitness: A Survey on Exercise Habits during Medical Education

Med Student Fitness\u27 investigates the exercise habits of students at NYMC. In particular, this survey compares the amount of cardiovascular and weightlifting workouts that students perform each week, as well as differences in gender, age, and year of program. Finally, an assessment of overall student fitness is given by the amount of students meeting the exercise suggestions provided by the American Medical Association

The Role of Bacteria-Particle Interactions in Marine Snow Dynamics

Marine snow aggregates are one of the primary vehicles for deep-sea carbon sequestration. Bacterial activity on marine snow affects both degradation and aggregation processes that determine the flux of carbon to depth, biogeochemical cycling, and microbial food webs. The microscale processes occurring on aggregates depend on specific interactions between bacteria and particles. In this thesis, I describe two such interactions which have larger scale implications on marine snow dynamics: (1) the effects of starvation on bacterial motility and colonization behaviors on marine aggregates and (2) interactions between bacteria and phytoplankton which could contribute to the production of TEP. Current models describing bacterial colonization on particles do not account for changes in bacterial behavior due to starvation, which may happen between successful encounters with particles and is a possible condition in the oligotrophic ocean. In my first study, I examine the effects of starvation on the colonization and detachment of several bacterial isolates on particles. I also describe the changes in bacterial motility resulting from starvation. Laboratory experiments on model aggregates indicate that responses to starvation are strain-specific, and can result in lower short-term steady-state bacterial abundances on the aggregates. Bacterial detachment from aggregates was unchanged. Motility data indicate that two of three strains tested had reduced swimming velocities, resulting in diffusivities six times lower in starved treatments than in fed treatments. This was corroborated by colonization data. Future models describing bacterial colonization should consider the shifting physiology and behavior of bacteria responding to starvation. In my second study, I investigated the interactions between bacterial isolates and the marine diatom Thalassiosira weissflogii (TW) on the production and characteristics of TEP, a major component of marine snow. One of two bacterial isolates (either Microscilla furvescens or Curacaobacter baltica) was added to jars of TW and incubated on a rolling table for seven days. During the time course, each jar was sampled for TEP length, area, total TEP, and bacterial distribution among the free-living and TEPassociated fractions. The two strains of bacteria showed different responses. Jars inoculated with Curacaobacter baltica had a significantly higher fraction of total bacteria that were associated with TEP, although the number of bacteria per unit area of TEP was lower. These results suggest that the strain-specific interactions between bacteria, phytoplankton, and TEP could impact the population distributions of bacteria. Over seven days, jars inoculated with Curacaobacter baltica produced more TEP; TEP coverage was almost four times higher (~8% of the total filter area) in jars inoculated with Curacaobacter baltica than those inoculated with Microscilla furvescens. Results from both studies stress the importance of strain-specific interactions in describing microscale processes. Integrating our understanding of responses of individual strains with information on the diversity and activities of bacterial communities on aggregates will better determine how these complex interactions may affect the fate of sinking aggregates and the solubilization of particles into dissolved organic matter

Global Patterns of Synchronization in Human Communications

Social media are transforming global communication and coordination. The data derived from social media can reveal patterns of human behavior at all levels and scales of society. Using geolocated Twitter data, we have quantified collective behaviors across multiple scales, ranging from the commutes of individuals, to the daily pulse of 50 major urban areas and global patterns of human coordination. Human activity and mobility patterns manifest the synchrony required for contingency of actions between individuals. Urban areas show regular cycles of contraction and expansion that resembles heartbeats linked primarily to social rather than natural cycles. Business hours and circadian rhythms influence daily cycles of work, recreation, and sleep. Different urban areas have characteristic signatures of daily collective activities. The differences are consistent with a new emergent global synchrony that couples behavior in distant regions across the world. A globally synchronized peak that includes exchange of ideas and information across Europe, Africa, Asia and Australasia. We propose a dynamical model to explain the emergence of global synchrony in the context of increasing global communication and reproduce the observed behavior. The collective patterns we observe show how social interactions lead to interdependence of behavior manifest in the synchronization of communication. The creation and maintenance of temporally sensitive social relationships results in the emergence of complexity of the larger scale behavior of the social system.Comment: 20 pages, 12 figures. arXiv admin note: substantial text overlap with arXiv:1602.0621

WISeREP - An Interactive Supernova Data Repository

We have entered an era of massive data sets in astronomy. In particular, the number of supernova (SN) discoveries and classifications has substantially increased over the years from few tens to thousands per year. It is no longer the case that observations of a few prototypical events encapsulate most spectroscopic information about SNe, motivating the development of modern tools to collect, archive, organize and distribute spectra in general, and SN spectra in particular. For this reason we have developed the Weizmann Interactive Supernova data REPository - WISeREP - an SQL-based database (DB) with an interactive web-based graphical interface. The system serves as an archive of high quality SN spectra, including both historical (legacy) data as well as data that is accumulated by ongoing modern programs. The archive provides information about objects, their spectra, and related meta-data. Utilizing interactive plots, we provide a graphical interface to visualize data, perform line identification of the major relevant species, determine object redshifts, classify SNe and measure expansion velocities. Guest users may view and download spectra or other data that have been placed in the public domain. Registered users may also view and download data that are proprietary to specific programs with which they are associated. The DB currently holds >8000 spectra, of which >5000 are public; the latter include published spectra from the Palomar Transient Factory, all of the SUSPECT archive, the Caltech-Core-Collapse Program, the CfA SN spectra archive and published spectra from the UC Berkeley SNDB repository. It offers an efficient and convenient way to archive data and share it with colleagues, and we expect that data stored in this way will be easy to access, increasing its visibility, usefulness and scientific impact.Comment: To be published in PASP. WISeREP: http://www.weizmann.ac.il/astrophysics/wiserep

Real-time Detection and Rapid Multiwavelength Follow-up Observations of a Highly Subluminous Type II-P Supernova from the Palomar Transient Factory Survey

The Palomar Transient Factory (PTF) is an optical wide-field variability survey carried out using a camera with a 7.8 deg^2 field of view mounted on the 48 inch Oschin Schmidt telescope at Palomar Observatory. One of the key goals of this survey is to conduct high-cadence monitoring of the sky in order to detect optical transient sources shortly after they occur. Here, we describe the real-time capabilities of the PTF and our related rapid multiwavelength follow-up programs, extending from the radio to the γ-ray bands. We present as a case study observations of the optical transient PTF10vdl (SN 2010id), revealed to be a very young core-collapse (Type II-P) supernova having a remarkably low luminosity. Our results demonstrate that the PTF now provides for optical transients the real-time discovery and rapid-response follow-up capabilities previously reserved only for high-energy transients like gamma-ray bursts