An Additive Basis for the Chow Ring of \bar{M}_{0,2}(P^r,2)

We begin a study of the intersection theory of the moduli spaces of degree two stable maps from two-pointed rational curves to arbitrary-dimensional projective space. First we compute the Betti numbers of these spaces using Serre polynomial and equivariant Serre polynomial methods developed by E. Getzler and R. Pandharipande. Then, via the excision sequence, we compute an additive basis for their Chow rings in terms of Chow rings of nonlinear Grassmannians, which have been described by Pandharipande. The ring structure of one of these Chow rings is addressed in a sequel to this paper.Comment: Published in SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at http://www.emis.de/journals/SIGMA

Early warning systems for malaria in Africa: from blueprint to practice.

Although the development of early warning systems for malaria has been advocated by international agencies and academic researchers for many years, practical progress in this area has been relatively modest. In two recent articles, Thomson et al. provide new evidence that models of malaria incidence that incorporate monitored or predicted climate can provide early warnings of epidemics one to five months in advance in semi-arid areas. Although the potential benefits of these models in terms of improved management of epidemics are clear, several technical and practical hurdles still need to be overcome before the models can be widely integrated into routine malaria-control strategies

Sub-femtosecond precision timing distribution, synchronization and coherent synthesis of ultrafast lasers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 180-189).In this thesis, we present a complete set of techniques for sub-femtosecond measurement, control and distribution of ultrafast optical pulse trains, with respect to pulse timing and phase. First, analytical analysis of the balanced optical cross-correlator (BOC) for attosecond precision pulse timing measurement is presented for both short and long crystal devices. It is found that the sensitivity of the long crystal BOC is independent of pulse duration, to first order. In addition, analytical noise models predict 13 as rms resolution, within a 1 MHz bandwidth, for optical pulses consistent with a practical fiber optic timing link. This analysis aids the widespread adoption of the BOC technique for other wavelengths and implementations. Secondly, long term timing distribution of a 200 MHz ultrafast optical pulse train over 340 m of single mode optical fiber is demonstrated, using the BOC. In this way, the group delay of the fiber link is directly stabilized with unprecedented precision and longterm stability. In addition, by distributing the entire optical pulse train, all optical and RF harmonics are provided at the remote location for direct synchronization of remote ultrafast lasers and microwave electronics. Over 168 hours of continuous, unaided operation, a drift of 5 fs rms is achieved, with less than 1.5 fs rms drift at timescales up to 10,000 seconds. Additional analysis of factors effecting performance, such as polarization mode dispersion and fiber nonlinearity is studied through experiment and simulations. It is found that nonlinear-origin drifts can be avoided for pulse energies below 40 pJ. A chirped pulse method could be implemented to distribute pulses of higher energy. Thirdly, the first quantum-resolution timing jitter measurement of ultrafast laser timing jitter for passively mode-locked lasers up to the Nyquist frequency is presented. The total jitter from for a 79.4 MHz stretched pulse erbium fiber laser is found to be 2.6 fs rms [10 kHz, 39.7 MHz]. It is found that the timing jitter power spectral density scales with frequency according to that expected for a white noise source, in agreement with theory. However, unexpected spurious jitter at high frequencies can occur for some mode-locked states, adding up to 5.5 fs rms jitter. Similar measurements of a 200 MHz erbium fiber soliton laser reveal the decay time of center frequency fluctuations to be 17 ns, with a predicted excess noise of approximately ten. These measurements suggest that timing jitter can be decreased through improved amplifier design. Finally, the synchronization of a 8 fs fiber supercontinuum at 1200 nm to a 7 fs Ti:Sapphire laser pulse train at 800 nm is achieved for both pulse timing and phase with attosecond precision. This achievement is enabled by the development of a novel scheme for stabilization of the carrier envelope offset of the entire optical bandwidth of an octave spanning supercontinuum, without introducing excess timing jitter. In particular, by implementing an acousto-optic frequency shifting (AOFS) feedback system within a fiber supercontinuum source, carrier envelope phase locking, to the Ti:Sapphire laser, is demonstrated to within 200 mrad rms [100 Hz, 5 MHz]. Previous techniques lack the high-speed, orthogonal control of CEP and pulse timing and broad optical bandwidth for synthesizing few-cycle optical pulses. Furthermore, timing synchronization of 280 as rms is achieved through combined piezoelectric and electro-optic feedback on the fiber supercontinuum, as measured with the BOC. This work enables the synthesis of a frequency comb spanning 650 to 1400 nm, resulting in a 3.5 fs transform limited pulse duration-assuming ideal spectral phase compression. To date, the spectrum has been successfully compressed to 4.7 fs, as measured with two-dimensional spectral shearing interferometry (2DSI). Moreover, by stabilizing a fiber supercontinuum source to a low-noise Ti:Sapphire laser, the ultra-high stability of the Ti:Sapphire laser is fully transferred to the octave spanning supercontinuum.by Jonathan A. Cox.Ph.D

Retention of native-like structure in an acyclic counterpart of a β-sheet antibiotic

AbstractAn acyclic derivative of the cyclic peptide antibiotic, ramoplanin, has been prepared. In aqueous solution, two-dimensional NMR spectroscopy indicates that the acyclic form adopts a threshold population of conformers in which at least part of the β-sheet characteristic of the intact ramoplanin persists. Thus, despite losing the entropic benefit which the macrocycle must lend to β-sheet formation, the polypeptide chain of the acyclic ramoplanin appears to display an innate tendency to adopt a native-like conformation

Mycobacterium abscessus: Environmental Bacterium Turned Clinical Nightmare

Mycobacteria are a large family of over 100 species, most of which do not cause diseases in humans. The majority of the mycobacterial species are referred to as nontuberculous mycobacteria (NTM), meaning they are not the causative agent of tuberculous (TB) or leprosy, i.e., Mycobacterium tuberculous complex and Mycobacterium leprae, respectively. The latter group is undoubtedly the most infamous, with TB infecting an estimated 10 million people and causing over 1.2 million deaths in 2017 alone TB and leprosy also differ from NTM in that they are only transmitted from person to person and have no environmental reservoir, whereas NTM infections are commonly acquired from the environment. It took until the 1950′s for NTM to be recognised as a potential lung pathogen in people with underlying pulmonary disease and another three decades for NTM to be widely regarded by the medical community when Mycobacterium avium complex was identified as the most common group of opportunistic pathogens in AIDS patients. This review focuses on an emerging NTM called Mycobacterium abscessus (M. abs). M. abs is a rapidly growing NTM that is responsible for opportunistic pulmonary infections in patients with structural lung disorders such as cystic fibrosis and bronchiectasis, as well as a wide range of skin and soft tissue infections in humans. In this review, we discuss how we came to understand the pathogen, how it is currently treated and examine drug resistance mechanisms and novel treatments currently in development. We highlight the urgent need for new and effective treatments for M. abs infection as well as improved in vivo methods of efficacy testing

Enhancing Water Quality Data Service Discovery And Access Using Standard Vocabularies

There is a growing need for consistency across the publishing, discovering, integrating and access to scientific datasets, such as water quality data. Such datasets may have varying formats and service interfaces. The Network Common Data Form (NetCDF) is both a software package and a data format for producing array-oriented scientific data, which is commonly used to exchange data, including water quality data. NetCDF datasets are also published through service interfaces using the THREDDS data server. Alternatively water quality datasets can be encoded with standard XML formats such as WaterML 2.0, which can be published with services such as the Open Geospatial Consortium (OGC) community\u27s Web Feature Service interface standard (WFS). However, appropriate interpretation of the content, discovery and interoperability of data depends on common models, schemas and vocabularies, though these may not always be available. Using the water quality vocabulary we have developed, formalized using the Resource Description Framework (RDF) language, and published as Linked Data, we demonstrate the use of such standard vocabularies in existing data services for providing service capability metadata. We also present methods for augmenting existing metadata fields for water quality data specifically in formats such as NetCDF, WaterML 2.0 using standard vocabularies. We show how using standard vocabularies that are encoded and published using semantic technologies can enhance discovery, integration and access to existing data services delivering water quality datasets

Tracking Cyber Adversaries with Adaptive Indicators of Compromise

A forensics investigation after a breach often uncovers network and host indicators of compromise (IOCs) that can be deployed to sensors to allow early detection of the adversary in the future. Over time, the adversary will change tactics, techniques, and procedures (TTPs), which will also change the data generated. If the IOCs are not kept up-to-date with the adversary's new TTPs, the adversary will no longer be detected once all of the IOCs become invalid. Tracking the Known (TTK) is the problem of keeping IOCs, in this case regular expressions (regexes), up-to-date with a dynamic adversary. Our framework solves the TTK problem in an automated, cyclic fashion to bracket a previously discovered adversary. This tracking is accomplished through a data-driven approach of self-adapting a given model based on its own detection capabilities. In our initial experiments, we found that the true positive rate (TPR) of the adaptive solution degrades much less significantly over time than the naive solution, suggesting that self-updating the model allows the continued detection of positives (i.e., adversaries). The cost for this performance is in the false positive rate (FPR), which increases over time for the adaptive solution, but remains constant for the naive solution. However, the difference in overall detection performance, as measured by the area under the curve (AUC), between the two methods is negligible. This result suggests that self-updating the model over time should be done in practice to continue to detect known, evolving adversaries.Comment: This was presented at the 4th Annual Conf. on Computational Science & Computational Intelligence (CSCI'17) held Dec 14-16, 2017 in Las Vegas, Nevada, US

General linear-optical quantum state generation scheme: Applications to maximally path-entangled states

We introduce schemes for linear-optical quantum state generation. A quantum state generator is a device that prepares a desired quantum state using product inputs from photon sources, linear-optical networks, and postselection using photon counters. We show that this device can be concisely described in terms of polynomial equations and unitary constraints. We illustrate the power of this language by applying the Grobner-basis technique along with the notion of vacuum extensions to solve the problem of how to construct a quantum state generator analytically for any desired state, and use methods of convex optimization to identify bounds to success probabilities. In particular, we disprove a conjecture concerning the preparation of the maximally path-entangled |n,0)+|0,n) (NOON) state by providing a counterexample using these methods, and we derive a new upper bound on the resources required for NOON-state generation.Comment: 5 pages, 2 figure