Exploratory Graphics of a Financial Dataset

company rating, default probability, support vector machines, colour coding

Nanoscale electrochemical patterning reveals the active sites for catechol oxidation at graphite surfaces

Graphite-based electrodes (graphite, graphene, and nanotubes) are used widely in electrochemistry, and there is a long-standing view that graphite step edges are needed to catalyze many reactions, with the basal surface considered to be inert. In the present work, this model was tested directly for the first time using scanning electrochemical cell microscopy reactive patterning and shown to be incorrect. For the electro-oxidation of dopamine as a model process, the reaction rate was measured at high spatial resolution across a surface of highly oriented pyrolytic graphite. Oxidation products left behind in a pattern defined by the scanned electrochemical cell served as surface-site markers, allowing the electrochemical activity to be correlated directly with the graphite structure on the nanoscale. This process produced tens of thousands of electrochemical measurements at different locations across the basal surface, unambiguously revealing it to be highly electrochemically active, with step edges providing no enhanced activity. This new model of graphite electrodes has significant implications for the design of carbon-based biosensors, and the results are additionally important for understanding electrochemical processes on related sp2-hybridized materials such as pristine graphene and nanotubes

Sensing Ocean, Ice and Land Reflected Signalsfrom Space: Results from the UK-DMC GPS Reflectometry Experiment

The use of Global Navigation Satellite System (GNSS) signals reflected from the Earth\u27s surface has progressed from its beginnings in the early 1990\u27s to a demonstrated practical linkage of measurements to geophysical characteristics of ocean, ice and land surfaces. A pioneering space-based experiment was carried on the UK-DMC satellite launched in September of 2003. The GPS receiver on the satellite was modified to accommodate a downward (nadir) pointing medium gain antenna and to send sampled IF data to a solid-state data recorder [1]. Since its launch it has been successfully used to target and detect specular reflections of GPS signals after scattering from the Earth\u27s oceans, ice sheetsand land surfaces. All data collections under a wide range of conditions have revealed reflected signals, including signals reflected off the ocean under reasonably rough ocean conditions. This demonstrates convincingly that GNSS Reflectometry (or GNSS Bistatic Radar) is a valid future technology for space based Earth remote sensing, even when using modest antenna gain configurations such as that deployed on the UK-DMC low Earth orbiting satellite. This paper presents a summary of the signals collected from over the ocean, and an examination of the signal relationship to the ocean wind and wave conditions is presented. The preliminary results from ice and land surfaces reflection analysis are also described. Reprinted with permission from The Institute of Navigation (http://ion.org/) and The Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation, (pp. 1679-1685). Fairfax, VA: The Institute of Navigation

Optical fibre digital pulse-position-modulation assuming a Gaussian received pulse shape

The abundance in bandwidth available in the best monomode fibres may be exchanged for improved receiver sensitivity by employing digital PPM. The paper presents a performance and optimisation analysis for a digital PPM coding scheme operating over a fibre channel employing a PIN-BJT receiver and assuming a Gaussian received pulse shape. The authors present original results for a 50 Mbit/s, 1.3 μm wavelength digital PPM system and conclude that, provided the fibre bandwidth is several times that of the data rate, digital PPM can outperform commercially available PIN-BJT binary PCM system

Nanoscale intermittent contact-scanning electrochemical microscopy

A major theme in scanning electrochemical microscopy (SECM) is a methodology for nanoscale imaging with distance control and positional feedback of the tip. We report the expansion of intermittent contact (IC)-SECM to the nanoscale, using disk-type Pt nanoelectrodes prepared using the laser-puller sealing method. The Pt was exposed using a focused ion beam milling procedure to cut the end of the electrode to a well-defined glass sheath radius, which could also be used to reshape the tips to reduce the size of the glass sheath. This produced nanoelectrodes that were slightly recessed, which was optimal for IC-SECM on the nanoscale, as it served to protect the active part of the tip. A combination of finite element method simulations, steady-state voltammetry and scanning electron microscopy for the measurement of critical dimensions, was used to estimate Pt recession depth. With this knowledge, the tip-substrate alignment could be further estimated by tip approach curve measurements. IC-SECM has been implemented by using a piezo-bender actuator for the detection of damping of the oscillation amplitude of the tip, when IC occurs, which was used as a tip-position feedback mechanism. The piezo-bender actuator improves significantly on the performance of our previous setup for IC-SECM, as the force acting on the sample due to the tip is greatly reduced, allowing studies with more delicate tips. The capability of IC-SECM is illustrated with studies of a model electrode (metal/glass) substrate

A Study into the Method of Precise Orbit Determination of a HEO Orbiter by GPS and Accelerometer

In the present day, orbit determination by Global Positioning System (GPS) is not unusual. Especially for low-cost small satellites, position determination by an on-board GPS receiver provides a cheap, reliable and precise method. However, the original purpose of GPS is for ground users, so the transmissions from all of the GPS satellites are directed toward the Earth s surface. Hence there are some restrictions for users above the GPS constellation to detect those signals. On the other hand, a desire for precise orbit determination for users in orbits higher than GPS constellation exists. For example, the next Japanese Very Long Baseline Interferometry (VLBI) mission "ASTRO-G" is trying to determine its orbit in an accuracy of a few centimeters at apogee. The use of GPS is essential for such ultra accurate orbit determination. This study aims to construct a method for precise orbit determination for such high orbit users, especially in High Elliptical Orbits (HEOs). There are several approaches for this objective. In this study, a hybrid method with GPS and an accelerometer is chosen. Basically, while the position cannot be determined by an on-board GPS receiver or other Range and Range Rate (RARR) method, all we can do to estimate the user satellite s position is to propagate the orbit along with the force model, which is not perfectly correct. However if it has an accelerometer (ACC), the coefficients of the air drag and the solar radiation pressure applied to the user satellite can be updated and then the propagation along with the "updated" force model can improve the fitting accuracy of the user satellite s orbit. In this study, it is assumed to use an accelerometer available in the present market. The effects by a bias error of an accelerometer will also be discussed in this paper

A Nanosatellite to Demonstrate GPS Oceanography Reflectometry

This paper describes a proposal for a rapid, low cost, nanosatellite mission to demonstrate the concept of GPS ocean reflectometry and to investigate the feasibility of determining sea state for a future operational space-based storm warning systems. The aims of this mission are to prove the general feasibility of GPS ocean reflectometry, to demonstrate sea state determination and to enable the development of a practical GPS ocean reflectometry payload for future missions. The payloads on the satellite consist of a 24 channel C/A code SGR-10 space GPS receiver and a solid state data recorder. The GPS receiver has one standard RHCP zenith antenna, and one high gain LHCP nadir antenna for receiving the reflected signals. A dual approach is taken to measurement gathering. Initially, bursts of directly sampled IF data are stored and downloaded to permit processing of the data on the ground. Later in the mission, the GPS receiver software may be modified to permit the processing of signals on-board the satellite. The nanosatellite is based on SSTL’s SNAP design and has a projected total mass of around 12 kilograms; orbit average power of approximately 4.8 watts; 3-axis attitude control to 1-2 degrees; VHF uplink, S-band downlink at 500 kbps, and OBC based on the StrongARM SA1100. Using the SNAP design enables a fast manufacture at low cost: estimated at 9 months and around 2 million Euros, including launch. The proposed mission makes use of the Surrey Space Centre Mission Control ground-station in Guildford (UK) for control and data gathering. Surrey Satellite Technology Ltd (SSTL) is a world leader in both nanosatellite and GPS technology for small satellites. SSTL’s highly successful SNAP-1 nanosatellite launched in June 2000 demonstrated the potential of such small spacecraft, and this proposal involves the first ever use of a nanosatellite for a commercial application (GANDER) in collaboration with SOS Ltd (UK) a company specialising in oceanography from space

An assessment of non-geophysical effects in spaceborne GNSS Reflectometry data from the UK TechDemoSat-1 mission

An assessment of non-geophysical effects in spaceborne global navigation satellite system reflectometry (GNSS-R) data from the UK TechDemoSat-1 (TDS-1) mission is presented. TDS-1 was launched in July 2014 and provides the first new spaceborne GNSS-R data since the pioneering UK-disaster monitoring constellation experiment in 2003. Non-geophysical factors evaluated include ambient L-band noise, instrument operating mode, and platform-related parameters. The findings are particularly relevant to users of uncalibrated GNSS-R signals for the retrieval of geophysical properties of the Earth surface. Substantial attitude adjustments of the TDS-1 platform are occasionally found to occur that introduce large uncertainties in parts of the TDS-1 GNSS-R dataset, particularly for specular points located outside the main beam of the nadir antenna where even small attitude errors can lead to large inaccuracies in the geophysical inversion. Out of eclipse however, attitude adjustments typically remain smaller than 1.5°, with larger deviations of up to 10° affecting less than 5% of the overall sun-lit data. Global maps of L1 ambient noise are presented for both automatic and programmed gain modes of the receiver, revealing persistent L-band noise hotspots along the Equator that can reach up to 2.5 dB, most likely associated with surface reflection of signals from other GNSS transmitters and constellations. Sporadic high-power noise events observed in certain regions point to sources of human origin. Relevant conclusions of this study are that platform attitude knowledge is essential and that radiometric calibration of GNSS-R signals should be used whenever possible. Care should be taken when considering using noise measurements over the equatorial oceans for calibration purposes, as ambient noise and correlated noise in delay–Doppler maps both show more variation than might be expected over these regions