New Horizons in Time-Domain Diffuse Optical Spectroscopy and Imaging

Jöbsis was the first to describe the in vivo application of near-infrared spectroscopy (NIRS), also called diffuse optical spectroscopy (DOS). NIRS was originally designed for the clinical monitoring of tissue oxygenation, and today it has also become a useful tool for neuroimaging studies (functional near-infrared spectroscopy, fNIRS). However, difficulties in the selective and quantitative measurements of tissue hemoglobin (Hb), which have been central in the NIRS field for over 40 years, remain to be solved. To overcome these problems, time-domain (TD) and frequency-domain (FD) measurements have been tried. Presently, a wide range of NIRS instruments are available, including commonly available commercial instruments for continuous wave (CW) measurements, based on the modified Beer–Lambert law (steady-state domain measurements). Among these measurements, the TD measurement is the most promising approach, although compared with CW and FD measurements, TD measurements are less common, due to the need for large and expensive instruments with poor temporal resolution and limited dynamic range. However, thanks to technological developments, TD measurements are increasingly being used in research, and also in various clinical settings. This Special Issue highlights issues at the cutting edge of TD DOS and diffuse optical tomography (DOT). It covers all aspects related to TD measurements, including advances in hardware, methodology, the theory of light propagation, and clinical applications

Even-Parity S_(N) Adjoint Method Including SP_(N) Model Error and Iterative Efficiency

In this Dissertation, we analyze an adjoint-based approach for assessing the model error of SP_(N) equations (low fidelity model) by comparing it against S_(N) equations (high fidelity model). Three model error estimation methods, namely, direct , residual, and adjoint methods are proposed. In order to compare the SP_(N) solution against S_(N), we also proposed angular intensity reconstruction schemes for reconstructing S_(N) angular intensity from SP_(N) solutions. The methodology is then applied to a vehicle atmosphere re-entry problem and the convergence behavior of the SP_(N) and Even-parity S_(N) are compared with that of the Least-squares S_(N) method. The results show that all the three model error estimation methods are equivalent up to a readily computable compensation and the Least-squares S_(N) method is far superior than the Even-parity S_(N) and SP_(N) methods when applied to such a near-void problem. Various forms of SP_(N) equations, together with their appropriate iterative solution schemes and acceleration techniques are evaluated in terms of iterative efficiency. The Fourier analyses and numerical test results indicate the Canonical form solved with DSA or AnMG preconditioned source iteration offering the best iterative performance

Hidden Citations Obscure True Impact in Science

References, the mechanism scientists rely on to signal previous knowledge, lately have turned into widely used and misused measures of scientific impact. Yet, when a discovery becomes common knowledge, citations suffer from obliteration by incorporation. This leads to the concept of hidden citation, representing a clear textual credit to a discovery without a reference to the publication embodying it. Here, we rely on unsupervised interpretable machine learning applied to the full text of each paper to systematically identify hidden citations. We find that for influential discoveries hidden citations outnumber citation counts, emerging regardless of publishing venue and discipline. We show that the prevalence of hidden citations is not driven by citation counts, but rather by the degree of the discourse on the topic within the text of the manuscripts, indicating that the more discussed is a discovery, the less visible it is to standard bibliometric analysis. Hidden citations indicate that bibliometric measures offer a limited perspective on quantifying the true impact of a discovery, raising the need to extract knowledge from the full text of the scientific corpus

Cold and Ultracold Molecules: Science, Technology, and Applications

This article presents a review of the current state of the art in the research field of cold and ultracold molecules. It serves as an introduction to the Special Issue of the New Journal of Physics on Cold and Ultracold Molecules and describes new prospects for fundamental research and technological development. Cold and ultracold molecules may revolutionize physical chemistry and few body physics, provide techniques for probing new states of quantum matter, allow for precision measurements of both fundamental and applied interest, and enable quantum simulations of condensed-matter phenomena. Ultracold molecules offer promising applications such as new platforms for quantum computing, precise control of molecular dynamics, nanolithography, and Bose-enhanced chemistry. The discussion is based on recent experimental and theoretical work and concludes with a summary of anticipated future directions and open questions in this rapidly expanding research field.Comment: 82 pages, 9 figures, review article to appear in New Journal of Physics Special Issue on Cold and Ultracold Molecule

Solar radiative transfer parameterizations for three-dimensional effects in cloudy atmospheres

This thesis addresses two major problems in the field of radiative transfer (RT) in the earth’s atmosphere. The first problem is linked with the need for significant computational resources of RT in a three-dimensional (3D) atmospheric model. Although only highly efficient one-dimensional (1D) RT models are employed for each pixel of the model domain separately and independently, it is still not possible to utilize these models on a frequent basis, compared to the rate at which meteorological variables are computed. That means that the calculated radiative properties (RP) are held constant for a longer period of time, while the prognostic meteorological variables are updated at a rapid rate. Even though there is no detailed study about the consequences of this disproportion, an attempt was made to develop an RT model which permits the fast computation of basic radiative transfer properties which could be used in the future to update this information more frequently. The developed model is based on the application of the radiative transfer perturbation theory to realistic cloud fields column by column. It turned out that the application, intended to replace the Independent Pixel Approximation (IPA), see below, is possible and promising within the assumptions and constraints of the utilized methods. It could be demonstrated that, depending on the actual case, errors in the pixel transmission and reflection stay bounded to values of up to 10%−15%. In one case the achieved acceleration could be investigated. It was about a factor of four compared to the direct application of the usual forward variant of the model, although no numerical optimization was carried out. The second problem concerns the realistic treatment of the 3D interactions of clouds and solar radiation. As implied in the above paragraph, 1D RT models are usually employed column by column which suppresses the exchange of radiation between those columns. Thus, fundamental 3D effects are neglected by this so-called Independent Pixel Approximation (IPA). These comprise not only small scale contributions due to diffuse radiative transport, but also large scale patterns like geometric effects of the inclined solar illumination. Examples are blurred radiative structures due to radiative smoothing and the shifted location of shadows and bright areas. To parameterize those effects strong efforts have been undertaken during the last couple of years. However, no method has proven to be completely satisfactory and ready for implementation. To carry this research one step further two approaches have been adopted and extended. The first is the concept of the Tilted Independent Pixel Approximation (TIPA). In contrast to the IPA, which ignores the solar geometry, this method correctly accounts for the slant illumination due to the correct tracking of the direct beam. As a result, the optical parameters in the slant columns are arranged in a more realistic order and the attenuation and the positions of the RP are less erroneous. To further improve this method a transformation has been developed which yields 3D resolution of the RP in the original grid. Since the TIPA still does not include any diffuse radiative exchange as another approach the Nonlocal Independent Pixel Approximation (NIPA) has been explored. This technique uses 1D results and carries out a convolution product to distribute RP across column boundaries. In order to arrive at a fully independent treatment of this method a simplified derivation of the convolution parameters was developed. Finally, TIPA and NIPA are combined to form NTIPA. These approaches have proven to be superior to IPA with respect to several aspects. The improvement ranges from several percent to 50% if maximum errors of the transmitted and reflected light are considered. Criteria like the distribution of the errors or the vertical profiles of the RP are also more preferable than their counterparts derived by IPA

Verification and Validation: High Charge and Energy (HZE) Transport Codes and Future Development

In the present paper, we give the formalism for further developing a fully three-dimensional HZETRN code using marching procedures but also development of a new Green's function code is discussed. The final Green's function code is capable of not only validation in the space environment but also in ground based laboratories with directed beams of ions of specific energy and characterized with detailed diagnostic particle spectrometer devices. Special emphasis is given to verification of the computational procedures and validation of the resultant computational model using laboratory and spaceflight measurements. Due to historical requirements, two parallel development paths for computational model implementation using marching procedures and Green s function techniques are followed. A new version of the HZETRN code capable of simulating HZE ions with either laboratory or space boundary conditions is under development. Validation of computational models at this time is particularly important for President Bush s Initiative to develop infrastructure for human exploration with first target demonstration of the Crew Exploration Vehicle (CEV) in low Earth orbit in 2008

Novel applications of Maxwell's equations to quantum and thermal phenomena

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 229-244).This thesis is concerned with the extension of Maxwell's equations to situations far removed from standard electromagnetism, in order to discover novel phenomena. We discuss our contributions to the efforts to describe quantum fluctuations, known as Casimir forces, in terms of classical electromagnetism. We prove that chirality in metamaterials can have no appreciable effect on the Casimir force, and design an alternative metamaterial in which the structure can have a strong effect on the Casimir force. We present a geometry that exhibits a repulsive Casimir force between metallic objects in vacuum, and describe our efforts to enhance this repulsive force using the numerical techniques that we and others developed. We then show how our techniques can be extended to study the physics of near-field radiative heat transfer, computing for the first time the exact heat transfer and power flux profiles between a plate and non-spherical objects. We find in particular that the heat flux profile is non-monotonic in separation from the cone tip. Finally, we demonstrate how techniques to compute photonic bandstructures in periodic systems can be extended to certain types of quasi-periodic structures, termed photonic-quasicrystals (PQCs).by Alexander P. McCauley.Ph.D