On Factors of Rank One Subshifts

Rank one subshifts are dynamical systems generated by a regular combinatorial process based on sequences of positive integers called the cut and spacer parameters. Despite the simple process that generates them, rank one subshifts comprise a generic set and are the source of many counterexamples. As a result, measure theoretic rank one subshifts, called rank one transformations, have been extensively studied and investigations into rank one subshifts been the basis of much recent work. We will answer several open problems about rank one subshifts. We completely classify the maximal equicontinuous factor for rank one subshifts, so that this factor can be computed from the parameters. We use these methods to classify when large classes of rank one subshifts have mixing properties. Also, we completely classify the situation when a rank one subshift can be a factor of another rank one subshift

Integration and Testing of the Nanosatellite Optical Downlink Experiment

CubeSat sensor performance continues to improve despite the limited size, weight, and power (SWaP) available on the platform. Missions are evolving into sensor constellations, demanding power-efficient high rate data downlink to compact and cost-effective ground terminals. SWaP constraints onboard nanosatellites limit the ability to accommodate large high gain antennas or higher power radio systems along with high duty cycle sensors. With the growing numbers of satellites in upcoming scientific, defense, and commercial constellations, it is difficult to place the high-gain burden solely on the ground stations, given the cost to acquire, maintain, and continuously operate facilities with dish diameters from 5 meters to 20 meters. In addition to the space and ground terminal hardware challenges, it is also increasingly difficult and sometimes not possible to obtain radio frequency licenses for CubeSats that require significant bandwidth. Free space optical communications (lasercom) can cost-effectively support data rates higher than 10 Mbps for similar space terminal SWaP as current RF solutions and with more compact ground terminals by leveraging components available for terrestrial fiber optic communication systems, and by using commercial amateur-astronomy telescopes as ground stations. We present results from the flight unit development, integration, and test of the Nanosatellite Optical Downlink Experiment (NODE) space terminal and ground station, scheduled for completion by summer of 2017. NODE’s objective is to demonstrate an end-to-end solution based on commercial telecommunications components and amateur telescope hardware that can initially compete with RF solutions at \u3e10 Mbps and ultimately scale to Gbps. The 1550 nm NODE transmitter is designed to accommodate platform pointing errors \u3c 3 degrees. The system uses an uplink beacon from the ground station and an onboard MEMS fine steering mirror to precisely point the 0.12 degree (2.1 mrad) 200 mW transmit laser beam toward the ground telescope. We plan to downlink to an estalblished ground terminal at the Jet Propulsion Laboratory (JPL) Optical Communications Telescope Laboratory (OCTL) ground station as well as the new low-cost 30 cm amateur telescope ground station design to reduce overall mission risk. Moving beyond our initial laboratory prototyping captured in Clements et al. 2016 we discuss recent progress developing and testing the flight electronics, opto-mechanical structures, and controls algorithms, including demonstration of a hardware-in-the-loop test of the fine pointing system, for both the space and ground terminals. We present results of over-the-air testing of the NODE system, as we advance from benchtop to hallway to rooftop demonstrations. We will present thermal and environmental test plans and discuss experimental as well as expected results

Nanosatellite optical downlink experiment: design, simulation, and prototyping

The nanosatellite optical downlink experiment (NODE) implements a free-space optical communications (lasercom) capability on a CubeSat platform that can support low earth orbit (LEO) to ground downlink rates>10  Mbps. A primary goal of NODE is to leverage commercially available technologies to provide a scalable and cost-effective alternative to radio-frequency-based communications. The NODE transmitter uses a 200-mW 1550-nm master-oscillator power-amplifier design using power-efficient M-ary pulse position modulation. To facilitate pointing the 0.12-deg downlink beam, NODE augments spacecraft body pointing with a microelectromechanical fast steering mirror (FSM) and uses an 850-nm uplink beacon to an onboard CCD camera. The 30-cm aperture ground telescope uses an infrared camera and FSM for tracking to an avalanche photodiode detector-based receiver. Here, we describe our approach to transition prototype transmitter and receiver designs to a full end-to-end CubeSat-scale system. This includes link budget refinement, drive electronics miniaturization, packaging reduction, improvements to pointing and attitude estimation, implementation of modulation, coding, and interleaving, and ground station receiver design. We capture trades and technology development needs and outline plans for integrated system ground testing.United States. National Aeronautics and Space Administration. Research Fellowship ProgramLincoln Laboratory (Lincoln Scholars)Lincoln Laboratory (Military Fellowship Program)Fundación Obra Social de La Caixa (Fellowship)Samsung FellowshipUnited States. Air Force (Assistant Secretary of Defense for Research & Engineering. Contract FAs872105C0002

Delineating the genotypic and phenotypic spectrum of HECW2-related neurodevelopmental disorders

Background Variants in HECW2 have recently been reported to cause a neurodevelopmental disorder with hypotonia, seizures and impaired language; however, only six variants have been reported and the clinical characteristics have only broadly been defined. Methods Molecular and clinical data were collected from clinical and research cohorts. Massive parallel sequencing was performed and identified individuals with a HECW2-related neurodevelopmental disorder. Results We identified 13 novel missense variants in HECW2 in 22 unpublished cases, of which 18 were confirmed to have a de novo variant. In addition, we reviewed the genotypes and phenotypes of previously reported and new cases with HECW2 variants (n=35 cases). All variants identified are missense, and the majority of likely pathogenic and pathogenic variants are located in or near the C-terminal HECT domain (88.2%). We identified several clustered variants and four recurrent variants (p.(Arg1191Gln);p.(Asn1199Lys);p.(Phe1327Ser);p.(Arg1330Trp)). Two variants, (p.(Arg1191Gln);p.(Arg1330Trp)), accounted for 22.9% and 20% of cases, respectively. Clinical characterisation suggests complete penetrance for hypotonia with or without spasticity (100%), developmental delay/intellectual disability (100%) and developmental language disorder (100%). Other common features are behavioural problems (88.9%), vision problems (83.9%), motor coordination/movement (75%) and gastrointestinal issues (70%). Seizures were present in 61.3% of individuals. Genotype-phenotype analysis shows that HECT domain variants are more frequently associated with cortical visual impairment and gastrointestinal issues. Seizures were only observed in individuals with variants in or near the HECT domain. Conclusion We provide a comprehensive review and expansion of the genotypic and phenotypic spectrum of HECW2 disorders, aiding future molecular and clinical diagnosis and management.Peer reviewe

Photography-based taxonomy is inadequate, unnecessary, and potentially harmful for biological sciences

The question whether taxonomic descriptions naming new animal species without type specimen(s) deposited in collections should be accepted for publication by scientific journals and allowed by the Code has already been discussed in Zootaxa (Dubois & Nemésio 2007; Donegan 2008, 2009; Nemésio 2009a–b; Dubois 2009; Gentile & Snell 2009; Minelli 2009; Cianferoni & Bartolozzi 2016; Amorim et al. 2016). This question was again raised in a letter supported by 35 signatories published in the journal Nature (Pape et al. 2016) on 15 September 2016. On 25 September 2016, the following rebuttal (strictly limited to 300 words as per the editorial rules of Nature) was submitted to Nature, which on 18 October 2016 refused to publish it. As we think this problem is a very important one for zoological taxonomy, this text is published here exactly as submitted to Nature, followed by the list of the 493 taxonomists and collection-based researchers who signed it in the short time span from 20 September to 6 October 2016

Il meticciato nell'Italia contemporanea. Storia, memorie e cultura di massa.

L'idea diffusa degli "italiani brava gente" e della diversit\ue0 della nostra storia rispetto alla storia USA, segnata da razzismo istituzionale, si fonda sul silenziamento del passato coloniale e razzista italiano. Il ripudio della categoria di razza da parte dell'Italia repubblicana e la smentita scientifica dell'esistenza biologica della categoria non hanno cancellato la presenza della razza, formazione storico-culturale che paradossalmente esiste e non esiste. Priva di referenti oggettivi nella realt\ue0, la razza produce in essa effetti significativi, opera sia come categoria sociale e strumento di esclusione, sia come costruzione simbolica e istanza identitaria. A fronte del silenziamento del meticciato storico nell'uso pubblico della storia e nella memoria nazionali del secondo dopoguerra, il saggio sottolinea la presenza diffusa del meticciato nei prodotti della cultura di massa italiani contemporanei e ne indaga i significati con gli strumenti degli studi critici sulla razza e in prospettiva comparata tra Italia e Stati Uniti

A jam-resistant CubeSat communications architecture

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017.Cataloged from PDF version of thesis.Includes bibliographical references (pages 133-140).This thesis proposes a communications system that utilizes the benefits of CubeSats to provide jam-resistant communications. The growth of CubeSats within educational communities has prompted their use in industry; both industry and academia have contributed towards making CubeSats much more capable. CubeSats can now perform many advanced missions, from technology demonstrations to Earth observation missions and science missions. Meanwhile, military satellite communications (MILSATCOM) continues to rely primarily on large, highly-capable satellites. CubeSats could augment MILSATCOM by providing many low-cost space terminals with short development times as a means to create a more robust communications suite. The CubeSat communications architecture proposed in this thesis aims to support mobile users in hostile environments who need to relay information to a command center. Jam-resistant communications are achieved by performing ground-based beam-forming (GBBF) on a radio-frequency (RF) uplink and relaying the information to a ground station via a laser communications (lasercom) downlink: each CubeSat acts as an element of a sparse antenna array. With the growth of free-space lasercom in the last decade, lasercom is now a reality on CubeSat-scale platforms. Lasercom systems have lower size, weight, and power (SWaP) compared to RF systems with similar data rates, making them a good fit for CubeSat platforms. GBBF is a special case of beamforming where each element of an antenna array relays its signal to a ground station for processing, minimizing complexity on the space terminal. Beam-forming provides anti-jamming capabilites due to the spacings between elements in the array, also known as spatial diversity. This spatial diversity allows spatial filtering to occur, which modifies the array's radiation pattern to mitigate interference, add gain to the main lobe, or add multiple beams. The system is designed with the goal of minimizing cost and development time, and two ways of accomplishing this are by supporting currently fielded handheld RF transmitters and by utilizing a lasercom downlink which is being developed as part of the Nanosatellite Optical Downlink Experiment (NODE) in MIT's Space, Telecommunications, Astronomy, and Radiation Lab (STARLab). This thesis builds on previous work done on the NODE project, specifically the waveform design for NODE. NODE is a 3U CubeSat demonstrating a lasercom down-link while in low Earth Orbit (LEO). NODE uses 200mW transmit power to obtain data rates from 8 Mbps to 80 Mbps. The Optical Communications Telescope Laboratory (OCTL) at the Jet Propulsion Laboratory (JPL) and an amateur telescope will be used as optical ground stations. In order to send information to the ground station, NODE uses a waveform that provides forward error correction (FEC) and interleaving to mitigate channel effects. This thesis develops the channel coding, interleaving, modulation, and framing approach employed in the NODE waveform to provide error-free communications. A Reed-Solomon code, selected because of its performance and the existence of open-source implementations, provides error-correction capabilities. NODE uses a one-second interleaver to combat the effects of channel fading when the laser beam passes through the atmosphere. The transmitter uses pulse position modulation (PPM), an intensity modulation scheme that uses the delay of a single pulse within a symbol time to transmit information, due to the advantages in using a duty-cycled waveform with an average-power limited optical amplifier. Since the delay of the pulse conveys information for PPM, the transmitter clock must be recovered in order to properly demodulate the received waveform, and NODE uses inter-symbol guard times to encode the transmitter clock onto the waveform. Python simulations are presented showing that the channel coding, interleaving, and modulation are sufficient to obtain error-free communications with a target channel bit error rate (BER) of 1 x 10-⁴. The modulator is implemented within a field programmable gate array (FPGA), and the design, validation, and testing of the modulator are described. The feasibility of performing GBBF on RF uplinks to CubeSats in LEO, where each CubeSat acts as an element of an adaptive array, is examined. The high Doppler and large spacing between CubeSats requires the use of a space-time-frequency adaptive processor (STFAP). The STFAP consists of Doppler and delay taps, complex weights, an adaptive processor, a polyphase filter bank, and a polyphase combiner. The STFAP becomes infeasible as the Doppler and delay spread between different CubeSats increases, and analysis is used to identify scenarios where the Doppler and delay spreads seen in LEO are acceptable. Systems Tool Kit (STK) simulations are performed to analyze the Doppler and delay environment in LEO. Two CubeSat formations and multiple orientations between a user and jammer are examined to determine cases where null-forming, a special case of beamforming, is effective. A constellation is necessary to provide global coverage and maximize the effectiveness of null-forming, and two possible constellations are discussed.by Caleb Kevin Ziegler.S.M