2,106 research outputs found
Aberrations in shift-invariant linear optical imaging systems using partially coherent fields
Here the role and influence of aberrations in optical imaging systems
employing partially coherent complex scalar fields is studied. Imaging systems
require aberrations to yield contrast in the output image. For linear
shift-invariant optical systems, we develop an expression for the output
cross-spectral density under the space-frequency formulation of statistically
stationary partially coherentfields. We also develop expressions for the output
cross{spectral density and associated spectral density for weak-phase,
weak-phase-amplitude, and single-material objects in one transverse spatial
dimension
Micro-Analysis of D/H Ratios in Mantle Minerals by Carrier-Gas Mass Spectrometry
Isotopic analysis of water released
by vacuum heating of hydrous minerals and sub-marine
basaltic glasses indicates that they vary in ÎŽD_(SMOW)
between ca. +10 and -115 per mil (e.g., [1]). However,
with few exceptions variations within that range are not
well correlated with other geochemical and geologic
properties and it is debated whether they reflect isotopic
heterogeneity in the mantle, fractionations produced
during ascent to the surface, or sub-solidus alteration.
This ambiguity is at least partly due to the
large sample size and slow rate of conventional analyses,
which precludes linking isotopic ranges to grain-scale
petrographic variables or constructing large data
bases (many 10âs of samples) in a reasonable period of
time. Ion microprobe methods provide one solution to
these problems, although they suffer from analytical
uncertainties nominally 5 to 10 times worse than conventional
measurements and large fractionations that
can be a source of systematic error
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Quantifying errors due to frequency changes and target location uncertainty for radar refractivity retrievals
Radar refractivity retrievals can capture near-surface humidity changes, but noisy phase changes of the ground clutter returns limit the accuracy for both klystron- and magnetron-based systems. Observations with a C-band (5.6 cm) magnetron weather radar indicate that the correction for phase changes introduced by local oscillator frequency changes leads to refractivity errors no larger than 0.25 N units: equivalent to a relative humidity change of only 0.25% at 20°C. Requested stable local oscillator (STALO) frequency changes were accurate to 0.002 ppm based on laboratory measurements. More serious are the random phase change errors introduced when targets are not at the range-gate center and there are changes in the transmitter frequency (ÎfTx) or the refractivity (ÎN). Observations at C band with a 2-ÎŒs pulse show an additional 66° of phase change noise for a ÎfTx of 190 kHz (34 ppm); this allows the effect due to ÎN to be predicted. Even at S band with klystron transmitters, significant phase change noise should occur when a large ÎN develops relative to the reference period [e.g., ~55° when ÎN = 60 for the Next Generation Weather Radar (NEXRAD) radars]. At shorter wavelengths (e.g., C and X band) and with magnetron transmitters in particular, refractivity retrievals relative to an earlier reference period are even more difficult, and operational retrievals may be restricted to changes over shorter (e.g., hourly) periods of time. Target location errors can be reduced by using a shorter pulse or identified by a new technique making alternate measurements at two closely spaced frequencies, which could even be achieved with a dualâpulse repetition frequency (PRF) operation of a magnetron transmitter
Atom-by-Atom Substitution of Mn in GaAs and Visualization of their Hole-Mediated Interactions
The discovery of ferromagnetism in Mn doped GaAs [1] has ignited interest in
the development of semiconductor technologies based on electron spin and has
led to several proof-of-concept spintronic devices [2-4]. A major hurdle for
realistic applications of (Ga,Mn)As, or other dilute magnetic semiconductors,
remains their below room-temperature ferromagnetic transition temperature.
Enhancing ferromagnetism in semiconductors requires understanding the
mechanisms for interaction between magnetic dopants, such as Mn, and
identifying the circumstances in which ferromagnetic interactions are maximized
[5]. Here we report the use of a novel atom-by-atom substitution technique with
the scanning tunnelling microscope (STM) to perform the first controlled atomic
scale study of the interactions between isolated Mn acceptors mediated by the
electronic states of GaAs. High-resolution STM measurements are used to
visualize the GaAs electronic states that participate in the Mn-Mn interaction
and to quantify the interaction strengths as a function of relative position
and orientation. Our experimental findings, which can be explained using
tight-binding model calculations, reveal a strong dependence of ferromagnetic
interaction on crystallographic orientation. This anisotropic interaction can
potentially be exploited by growing oriented Ga1-xMnxAs structures to enhance
the ferromagnetic transition temperature beyond that achieved in randomly doped
samples. Our experimental methods also provide a realistic approach to create
precise arrangements of single spins as coupled quantum bits for memory or
information processing purposes
XTE J0111.2-7317 : a nebula-embedded X-ray binary in the SMC
The observed characteristics of the nebulosity surrounding the SMC High Mass
X-ray Binary XTE J0111.2-7317 are examined in the context of three possible
nebular types: SNR, bowshock and HII region. Observational evidence is
presented which appears to support the interpretation that the nebulosity
surrounding XTE J0111.2-7317 is an HII region. The source therefore appears to
be a normal SMC Be X-ray binary (BeXRB) embedded in a locally enhanced ISM
which it has photoionised to create an HII region. This is supported by
observations of the X-ray outburst seen with BATSE and RXTE in 1998-1999. It
exhibited characteristics typical of a giant or type II outburst in a BeXRB
including large spin-up rates, Lx~10E38 erg/sq.cm-s, and a correlation between
spin-up rate and pulsed flux. However, the temporal profile of the outburst was
unusual, consisting of two similar intensity peaks, with the first peak of
shorter duration than the second.Comment: Accepted for publication by MNRA
Model and Sensor-Based Recommendation Approaches for In-Season Nitrogen Management in Corn
Nitrogen management for corn (Zea mays L.) may be improved by applying a portion of N in-season. This investigation was conducted to evaluate crop modeling (Maize-N) and active crop canopy sensing approaches for recommending in-season N fertilizer rates. These approaches were evaluated during 2012â2013 on 11 field sites, in Missouri, Nebraska, and North Dakota. Nitrogen management also included a no-N treatment (check) and a non-limiting N reference (all at planting). Nitrogen management treatments were assessed for two hybrids and at low and high seeding rates, arranged in a randomized complete block design. In 9 of 11 site-years, the sensor-based approach recommended lower in-season N rates than the model (collectively 59% less N), resulting in trends of higher partial factor productivity of nitrogen (PFPN) and higher agronomic efficiency (AE) than the model. However, yield was better protected by the model-based approach. In some situations, canopy sensing excelled at optimizing the N rate for localized conditions. With abnormally warm and moist soil conditions for the 2012 Nebraska sites and presumed high levels of inorganic N from mineralization, N application was appropriately reduced, resulting in no yield decrease and N savings compared to the non-limiting N reference. Depending on the site, both recommendation approaches were successful; a combination of model and sensor information may optimize in-season decision support for N recommendation
Sceptical Employees as CSR Ambassadors in Times of Financial Uncertainty
This chapter offers new insights into the understanding of internal (employee) perceptions of organizational corporate social responsibility (CSR) policies and strategies. This study explores the significance of employeesâ involvement and scepticism upon CSR initiatives and focuses on the effects it may have upon word of mouth (WOM) and the development of employeeâorganisation relationships. Desk research introduces the research questions. Data for the research questions were gathered through a self-completion questionnaire distributed in a hardcopy form to the sample. An individualâs level of scepticism and involvement appears to affect the development of a positive effect on employeesâ WOM. Involvement with the domain of the investment may be a central factor affecting relationship building within the organization, and upon generation of positive WOM. The chapter offers a conceptual framework to public relations (PR) and corporate communications practitioners, which may enrich their views and understanding of the use and value of CSR for communication strategies and practices. For-profit organisations are major institutions in todayâs society. CSR is proffered as presenting advantages for (at macro level) society and (micro level) the organization and its employees. Concepts, such as involvement and scepticism, which have not been rigorously examined in PR and corporate communication literature, are addressed. By examining employee perceptions, managers and academic researchers gain insights into the acceptance, appreciation and effectiveness of CSR policies and activities upon the employee stakeholder group. This will affect current and future CSR communication strategies. The knowledge acquired from this chapter may be transferable outside the for-profit sector
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