Preflight SL-1/SL-3 Skylab VHF ranging coverage (nominal TPI). Antenna and propagation studies for spacecraft systems, task E-531

A preflight assessment of the Skylab VHF ranging coverage for the rendezvous portion of the nominal SL-1/SL-3 mission is reported, assuming a 27 July 1973 SL-3 launch. Data are based on a nominal attitude trajectory, which has the Saturn workshop in a solar inertial attitude throughout the rendezvous; the CSM terminal phase initiation maneuver is nominal. An addendum to this report is being prepared, which considers the effects of early and late TPI maneuvers. Curves are presented which show the variation in received power levels on both spacecraft-to-spacecraft links from about 600 n.mi. range to CSM and SWS station keeping. Appropriate threshold levels are shown on these received power curves to indicate zero circuit margins for the ranging function

Antenna and propagation studies for spacecraft systems: Addendum to preflight SL-1/SL-3 Skylab VHF ranging coverage (early and late TPI)

A preflight assessment is presented of the expected Skylab VHF ranging coverage for the rendezvous portion of the SL-1/SL-3 mission, assuming a 28 July 1973 launch date, for the alternative trajectory cases characterized by either an early TPI or a late TPI. In this assessment early TPI and late TPI are used to indicate a TPI maneuver occurring 10 minutes prior to or after the nominally scheduled TPI maneuver, respectively. The Saturn workshop (SWS) maintains a solar inertial (SI) attitude throughout rendezvous for both trajectory cases. The results summarized concern VHF ranging function performance during that period most likely to be affected by off-nominal TPI conditions, i.e., NSR (5:56 g.e.t.) to station keeping. Curves are presented which show the variation in received power levels on both spacecraft-to-spacecraft links from about 100 n.mi. range to CSM and SWS station keeping. Appropriate threshold levels are shown on these received power curves to indicate zero circuit margins for the ranging function

Near-Infrared spectroscopy of the super star cluster in NGC1705

We study the near-infrared properties of the super star cluster NGC1750-1 in order to constrain its spatial extent, its stellar population and its age. We use adaptive optics assisted integral field spectroscopy with SINFONI on the VLT. We estimate the spatial extent of the cluster and extract its K-band spectrum from which we constrain the age of the dominant stellar population. Our observations have an angular resolution of about 0.11", providing an upper limit on the cluster radius of 2.85+/-0.50 pc depending on the assumed distance. The K-band spectrum is dominated by strong CO absorption bandheads typical of red supergiants. Its spectral type is equivalent to a K4-5I star. Using evolutionary tracks from the Geneva and Utrecht groups, we determine an age of 12+/-6 Myr. The large uncertainty is rooted in the large difference between the Geneva and Utrecht tracks in the red supergiants regime. The absence of ionized gas lines in the K-band spectrum is consistent with the absence of O and/or Wolf-Rayet stars in the cluster, as expected for the estimated age.Comment: 5 pages, 4 figures. Research Note accepted in Astronomy and Astrophysic

Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)

The accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin.) is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02)‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C associated with salinities below 33.0 (±0.5)‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin.), becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability

Mitigating optical losses in crystalline silicon thin film solar cells on glass

Liquid phase crystallized silicon thin film solar cells on glass provide efficiencies up to 14.2 . While open circuit voltage and fill factor are already comparable to wafer based devices, short circuit current density is reduced due to incomplete light absorption. This paper analyzes the losses of current device designs in experiment and one dimensional simulations, revealing the low absorber thickness of 15 20 amp; 956;m as well as the planar glass silicon interface as the main cause of non absorption. Interface textures, in particular a sinusoidal texture and a smooth anti reflective three dimensional SMART texture, are discussed concerning their potential to mitigate these losses, allowing to reduce losses at the glass silicon interface by at least 40 relative. Taking the electronic interface quality into account, the SMART texture is identified as the most promising texture for light management in liquid phase crystallized silicon thin film solar cells on glas

Fifa-isation: Spatial security, sponsor protection and media management at the 2010 World Cup

This paper presents a case-study of spatial brand protection and media management and security strategies at the 2010 Football World Cup (FWC) in South Africa (RSA). This focus stems from the realisation that commercially designated event spaces are very important environments for the interests of FWC sponsors, and that the media has a pivotal role in conveying messages about desirable conduct in such environments. In these respects, stakeholder organisations are concerned about safeguarding core event spaces, and with promoting positive messages about the FWC via the media. The paper therefore investigates the interests of key stakeholders at the 2010 FWC: the event owner Fédération Internationale de Football Association (FIFA), the FWC sponsors and the host city (Cape Town). It is concerned with identifying various surveillance strategies to manage public spaces at the FWC, albeit with a particular emphasis on protecting the interests of sponsors and their brand integrity. It is also concerned with strategies to manage the media at the FWC, with a particular emphasis on how FIFA stymies dissent and forces compliance among reporters and news outlets that undermine critical surveillance into these practices of spatial management. Taken together, these hyper-protectionist appr oaches demonstrate what we have described as the FIFA-isation of the FWC, where commercial risk is outsourced to the event host, while the commercial benefits flow back to the event owner. Concomitantly, FIFA makes enormous surveillance demands on the event hosts and those residing in the country and city where it is to be held, and upon the media that broadcast and report on the world's biggest sports mega events. © The author(s), 2014

Antireflective nanotextures for monolithic perovskite silicon tandem solar cells

Recently, we studied the effect of hexagonal sinusoidal textures on the reflective properties of perovskite silicon tandem solar cells using the finite element method FEM . We saw that such nanotextures, applied to the perovskite top cell, can strongly increase the current density utilization from 91 for the optimized planar reference to 98 for the best nanotextured device period 500 nm and peak to valley height 500 nm , where 100 refers to the Tiedje Yablonovitch limit. [D. Chen et al., J. Photonics Energy 8, 022601, 2018 , doi 10.1117 1.JPE.8.022601] In this manuscript we elaborate on some numerical details of that work we validate an assumption based on the Tiedje Yablonovitch limit, we present a convergence study for simulations with the finite element method, and we compare different configurations for sinusoidal nanotexture

Improved Light Management in Crystalline Silicon Thin Film Solar Cells by Advanced Nano Texture Fabrication

We present a texturing method for liquid phase crystallized silicon thin film solar cells enabling a maximum achievable short circuit current density of 36.5mA cm 2 due to optimized light management compared to current textured device

Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint

Perovskite silicon tandem solar cells are the most promising concept for a future photovoltaic technology. We report on recent progress from an optical viewpoint and disucss how we achieved more than 25 device efficienc

Tailoring nano textures for optimized light in coupling in liquid phase crystallized silicon thin film solar cells

Thin film solar cells based on liquid phase crystallized silicon LPC Si with 8 20 m thick absorber layers demand for advanced light management to achieve high photocurrent densities. Open circuit voltages Voc gt;600 mV underline the high silicon material quality of LPC silicon thin films on nano textured glass superstrates. We present a 500 nm pitched sinusoidal nano texture which outperforms larger pitched gratings with respect to light in coupling at the buried glass silicon interface. In the wavelength range of interest reflection of incident light is minimized to values close to 4 , which is the reflection at the sun facing air glass interface. Further, the electronic material quality of sinusoidally textured devices is analyzed on basis of a comparison of maximum achieved open circuit voltages on different texture types. The Voc on sinusoidally textured glass superstrates could be raised to 630 mV by changing the interlayer deposition method from a PVD to a PECVD process. Thus, we are able to unify high optical and electronic properties of silicon absorber layers on sinusoidal textured glass substrates. These results constitute a crucial step towards fully exploiting the optical potential of LPC silicon thin film solar cell