bluuebunny/crossref_metadata_2025 huggingface dataset:
Silver fluorescent x‐ray yield and its influence on the dose rate constant for nine low‐energy brachytherapy source models
Authors: Nath Ravinder , Chen Zhe Jay
Published: October 2007

The physical characteristics of the photons emitted by a low‐energy brachytherapy source are strongly dependent on the source's construction. Aside from absorption and scattering caused by the internal structures and the source encapsulation, the photoelectric interactions occurred in certain type of source‐construction materials can generate additional energetic characteristic x rays with energies different from those emitted by the bare radionuclide. As a result, the same radionuclide encapsulated in different source models can result in dose rate constants and other dosimetric parameters that are strikingly different from each other. The aim of this work was to perform a systematic study on the yield of silver fluorescent x rays produced in nine sources that are known to contain silver and its impact on the dose‐rate constant. Using a high‐resolution germanium spectrometer, the relative spectra emitted by the nine sources on its bisector were measured and found to be similar to each other (the maximum variation in the relative intensity was less than 4%). On the other hand, the measured silver fluorescent x‐ray spectra exhibited much greater variations from model to model; the maximum change in the measured relative intensity was over 95%. This larger variation in the measured silver fluorescent x‐ray yield was caused by (1) the different amount of silver that was directly exposed to the radionuclide in different source models and (2) the stronger influence of the source's internal geometry on the silver fluorescent x rays. Because the addition of silver fluorescent x rays can significantly alter the photon characteristics emitted by the radioactive sources, a precise knowledge on the silver fluorescent x‐ray yield is needed in theoretical calculations of the sources’ intrinsic dosimetric properties. This study concludes that the differences in silver fluorescent yield are the primary causes of the variable dose rate constant observed among these source models.
Breast cancer detection using neutron stimulated emission computed tomography: Prominent elements and dose requirements
Authors: Bender Janelle E. , Kapadia Anuj J. , Sharma Amy C. , Tourassi Georgia D. , Harrawood Brian P. , Floyd Carey E.
Published: October 2007

Neutron stimulated emission computed tomography (NSECT) is being developed to noninvasively determine concentrations of trace elements in biological tissue. Studies have shown prominent differences in the trace element concentration of normal and malignant breast tissue. NSECT has the potential to detect these differences and diagnose malignancy with high accuracy with dose comparable to that of a single mammogram. In this study, NSECT imaging was simulated for normal and malignant human breast tissue samples to determine the significance of individual elements in determining malignancy. The normal and malignant models were designed with different elemental compositions, and each was scanned spectroscopically using a simulated neutron beam. The number of incident neutrons was varied from 0.5 million to 10 million neutrons. The resulting gamma spectra were evaluated through receiver operating characteristic (ROC) analysis to determine which trace elements were prominent enough to be considered markers for breast cancer detection. Four elemental isotopes (, , , and ) at five energy levels were shown to be promising features for breast cancer detection with an area under the ROC curve above 0.85. One of these elements— at —achieved perfect classification at 10 million incident neutrons and could be detected with as low as 3 million incident neutrons. Patient dose was calculated for each gamma spectrum obtained and was found to range from between 0.05 and depending on the number of neutrons. This simulation demonstrates that NSECT has the potential to noninvasively detect breast cancer through five prominent trace element energy levels, at dose levels comparable to other breast cancer screening techniques.
Impact of target‐to‐background ratio, target size, emission scan duration, and activity on physical figures of merit for a 3D LSO‐based whole body PET/CT scanner
Authors: Brambilla M. , Matheoud R. , Secco C. , Sacchetti G. , Comi S. , Rudoni M. , Carriero A. , Inglese E.
Published: October 2007

The aim of our work is to describe the way in which physical figures of merit such as contrast‐to‐noise ratio (CNR) behave when varying acquisition parameters such as emission scan duration (ESD) or activity at the start of acquisition that in clinical practice can be selected by the user, or object properties such as target dimensions or target‐to‐background (T/B) ratio, which depend uniquely on the intrinsic characteristics of the object being imaged. Figures of merit, used to characterize image quality and quantitative accuracy for a 3D‐LSO based PET/CT scanner, were studied as a function of ESD and for different target sizes and T/B ratios using a multivariate approach in a wide range of conditions approaching the ones that can be encountered in clinical practice. An annular ring of water bags of thickness was fitted over an IEC phantom in order to obtain counting rates similar to those found in average patients. The average scatter fraction (SF) of the modified IEC phantom was similar to the mean SF measured on patients with a similar scanner. A supplemental set of micro‐hollow spheres was positioned inside the phantom. The NEMA NU 2‐2001 scatter phantom was positioned at the end of the IEC phantom to approximate the clinical situation of having activity that extends beyond the scanner. The phantoms were filled with a solution of water and and the spheres with various T/B ratios of 22.5, 10.3, and 3.6. Sequential imaging was performed to acquire PET images with varying background activity concentrations of about 12, 9, 6.4, 5.3, and , positioned on the linear portion of the phantom's NECR curve, well below peak NECR of that is reached at . The ESD was set to 1, 2, 3, and . With T/B ratios of 3.6, 10.3, and 22.5, the 13.0, 8.1, and spheres were detectable for the whole ranges of background activity concentration and ESD, respectively. The ESD resulted as the most significant predictor of CNR variance, followed by T/B ratio and the cross sectional area of the given sphere. Only last comes with a weight more than halved with respect to ESD. Thus, raising ESD seems to be much more effective than raising in order to obtain higher CNR, which is the physical figure of merit closely related with target detectability, at least in the simple task of the signal known exactly background known exactly model.
Does image quality matter? Impact of resolution and noise on mammographic task performance
Authors: Saunders Robert S. , Baker Jay A. , Delong David M. , Johnson Jeff P. , Samei Ehsan
Published: October 2007

The purpose of this study was to examine the effects of different resolution and noise levels on task performance in digital mammography. This study created an image set with images at three different resolution levels, corresponding to three digital display devices, and three different noise levels, with noise magnitudes similar to full clinical dose, half clinical dose, and quarter clinical dose. The images were read by five experienced breast imaging radiologists. The data were then analyzed to compute two accuracy statistics (overall classification accuracy and lesion detection accuracy) and performance at four diagnostic tasks (detection of microcalcifications, benign masses, malignant masses, and discrimination of benign and malignant masses). Human observer results showed decreasing display resolution had little effect on overall classification accuracy and individual diagnostic task performance, but increasing noise caused overall classification accuracy to decrease by a statistically significant 21% as the breast dose went to one quarter of its normal clinical value. The noise effects were most prominent for the tasks of microcalcification detection and mass discrimination. When the noise changed from full clinical dose to quarter clinical dose, the microcalcification detection performance fell from 89% to 67% and the mass discrimination performance decreased from 93% to 79%, while malignant mass detection performance remained relatively constant with values of 88% and 84%, respectively. As a secondary aim, the image set was also analyzed by two observer models to examine whether their performance was similar to humans. Observer models differed from human observers and each other in their sensitivity to resolution degradation and noise. The primary conclusions of this study suggest that quantum noise appears to be the dominant image quality factor in digital mammography, affecting radiologist performance much more profoundly than display resolution.
Sensitivities in the production of spread‐out Bragg peak dose distributions by passive scattering with beam current modulation
Authors: Lu Hsiao‐Ming , Brett Robert , Engelsman Martijn , Slopsema Roelf , Kooy Hanne , Flanz Jay
Published: October 2007

A spread‐out Bragg peak (SOBP) is used in proton beam therapy to create a longitudinal conformality of the required dose to the target. In order to create this effect in a passive beam scattering system, a variety of components must operate in conjunction to produce the desired beam parameters. We will describe how the SOBP is generated and will explore the tolerances of the various components and their subsequent effect on the dose distribution. A specific aspect of this investigation includes a case study involving the use of a beam current modulated system. In such a system, the intensity of the beam current can be varied in synchronization with the revolution of the range‐modulator wheel. As a result, the weights of the pulled‐back Bragg peaks can be individually controlled to produce uniform dose plateaus for a large range of treatment depths using only a small number of modulator wheels.
An investigation of beam parameters for Co‐60 tomotherapy
Authors: Cadman Pat
Published: October 2007

The effect of various physical beam parameters for Co‐60 tomotherapy is examined, including: Cylindrical source size, source‐to‐collimator distance (SCD) and collimator leaf width. In general, beam profile effects are seen with larger Co‐60 sources that are not seen with conventional linacs and multileaf collimators that are used for IMRT, including a broadening of the profile width as the source width increases. A treatment planning study was conducted to evaluate the effect of various beam parameter combinations with planning regions of interest typical of a simultaneous boost head and neck treatment. Combinations of SCD and source FWHM that produce an 80%–20% profile distance less than approximately at depth produced a Co‐60 tomotherapy plan with better DVH results than a conventional 7‐field linac plan for a leaf width. Further improvement may be achieved by reducing the leaf width. In general it may be concluded that commercially available cylindrical Co‐60 sources of diameter may be appropriate for tomotherapy if the proper combination of beam parameters is chosen.
A practical method to determine the healing and cooling curves of x‐ray tube assemblies
Authors: Bottaro M. , Moralles M. , Viana V. , Donatiello G. L. , Silva E. P.
Published: October 2007

A practical method to determine the heating and cooling curves of x‐ray tube assemblies with rotating anode x‐ray tube is proposed. Available procedures to obtain these curves as described in the literature are performed during operation of the equipment, and the precision of the method depends on the knowledge of the total energy applied in the system. In the present work we describe procedures which use a calorimetric system and do not require the operation of the x‐ray equipment. The method was applied successfully to a x‐ray tube assembly that was under test in our laboratory.
IMRT planning and delivery incorporating daily dose from mega‐voltage cone‐beam computed tomography imaging
Authors: Miften Moyed , Gayou Olivier , Reitz Bodo , Fuhrer Russell , Leicher Brian , Parda David S.
Published: October 2007

The technology of online mega‐voltage cone‐beam (CB) computed tomography (MV‐CBCT) imaging is currently used in many institutions to generate a 3D anatomical dataset of a patient in treatment position. It utilizes an accelerator therapy beam, delivered with 200° gantry rotation, and captured by an electronic portal imager to account for organ motion and setup variations. Although the patient dose exposure from a single volumetric MV‐CBCT imaging procedure is comparable to that from standard double‐exposure orthogonal portal images, daily image localization procedures can result in a significant dose increase to healthy tissue. A technique to incorporate the daily dose, from a MV‐CBCT imaging procedure, in the IMRT treatment planning optimization process was developed. A composite IMRT plan incorporating the total dose from the CB was optimized with the objective of ensuring uniform target coverage while sparing the surrounding normal tissue. One head and neck cancer patient and four prostate cancer patients were planned and treated using this technique. Dosimetric results from the prostate IMRT plans optimized with or without CB showed similar target coverage and comparable sparing of bladder and rectum volumes. Average mean doses were higher by for the bladder and comparable for the rectum . In addition, an average mean dose increase of in the femoral heads and in irradiated tissue was observed. However, the and values for bladder and rectum were lower by and indicating better volume sparing at high doses with the optimized plans incorporating CB. For the head and neck case, identical target coverage was achieved, while a comparable sparing of the brain stem, optic chiasm, and optic nerves was observed. The technique of optimized planning incorporating doses from daily online MV‐CBCT procedures provides an alternative method for imaging IMRT patients. It allows for daily treatment modifications where other volumetric tomographic imaging techniques may not be feasible and/or available and where accurate patient localization with a high degree of precision is required.
BGRT: Biologically guided radiation therapy—The future is fast approaching!
Authors: Stewart Robert D. , Li X. Allen
Published: October 2007

Rapid advances in functional and biological imaging, predictive assays, and our understanding of the molecular and cellular responses underpinning treatment outcomes herald the coming of the long‐sought goal of implementing patient‐specific biologically guided radiation therapy (BGRT) in the clinic. Biological imaging and predictive assays have the potential to provide patient‐specific, three‐dimensional information to characterize the radiation response characteristics of tumor and normal structures. Within the next decade, it will be possible to combine such information with advanced delivery technologies to design and deliver biologically conformed, individualized therapies in the clinic. The full implementation of BGRT in the clinic will require new technologies and additional research. However, even the partial implementation of BGRT treatment planning may have the potential to substantially impact clinical outcomes.
Effect of beam number on organ‐at‐risk sparing in dynamic multileaf collimator delivery of intensity modulated radiation therapy
Authors: Popple Richard A. , Fiveash John B. , Brezovich Ivan A.
Published: October 2007

Due to practical limitations such as inter‐ and intraleaf transmission, nondivergent leaf end design, and leaf scatter, multileaf collimators (MLCs) are unable to accurately produce the ideal fluence patterns generated by inverse planning systems. Consequently, low dose regions receive substantially more radiation than they would with an ideal MLC that could generate the desired fluence pattern. Previous work by others has found that the discrepancy between desired and actual fluence patterns produced by an MLC increases rapidly with increasing complexity of the desired fluence map. In addition to the complexity of individual fluence maps, other parameters can contribute to the overall complexity of a treatment plan, most notably the number of beams. In this work, we investigate the effect of beam number on critical structure sparing for dynamic MLC delivered intensity modulated radiation therapy. Six cases from each of two challenging clinical sites, previously irradiated head and neck and paraspinal metastasis, were planned with the goal of minimizing the spinal cord dose. Plans were developed for five to 27 beams. All plans were renormalized such that the target volume receiving the prescription dose was the same for all plans of each site. For each case, we calculated the spinal cord (the dose such that of normal tissue receives greater than or equal to ), normal tissue , the normal tissue mean dose, and the standard deviation of dose in the planning target volume (PTV). For the head and neck cases, the mean increase in spinal cord between seven and 27 beam plans was 10% of the prescription dose, whereas for the paraspinal case, the increase was 2.6%. For the head and neck cases, the mean decrease in normal tissue between seven and 11 beam plans was 2.6% and was constant for more than 11 beams. For the paraspinal cases, the mean decrease in normal tissue between seven and 27 beam plans was 3.7%. The mean normal tissue dose was approximately independent of the number of beams for both sites. For the head and neck cases, the PTV standard deviation was independent of the number of beams, while for the paraspinal cases it decreased by an average of 1.8% from seven to 27 beams. Calculations for seven and 27 beams in which the MLC transmission was varied from 0% to 2% demonstrated that the increase in spinal cord with increasing number of beams is largely due to MLC transmission, which is not included in the optimization. Increasing the number of beams increased the critical structure dose, although decreasing beam number results in increasing normal tissue and target dose heterogeneity. The optimal tradeoff is dependent on the clinical situation, but seems to be seven to nine beams. Beam geometry optimization may reduce the number of beams required to provide adequate target coverage, thus limiting critical structure dose.
Internal‐external correlation investigations of respiratory induced motion of lung tumors
Authors: Ionascu Dan , Jiang Steve B. , Nishioka Seiko , Shirato Hiroki , Berbeco Ross I.
Published: October 2007

In gated radiation therapy procedures, the lung tumor position is used directly (by implanted radiopaque markers) or indirectly (by external surrogate methods) to decrease the volume of irradiated healthy tissue. Due to a risk of pneumothorax, many clinics do not implant fiducials, and the gated treatment is primarily based on a respiratory induced external signal. The external surrogate method relies upon the assumption that the internal tumor motion is well correlated with the external respiratory induced motion, and that this correlation is constant in time. Using a set of data that contains synchronous internal and external motion traces, we have developed a dynamic data analysis technique to study the internal‐external correlation, and to quantitatively estimate its underlying time behavior. The work presented here quantifies the time dependent behavior of the correlation between external respiratory signals and lung implanted fiducial motion. The corresponding amplitude mismatch is also reported for the lung patients studied. The information obtained can be used to improve the accuracy of tumor tracking. For the ten patients in this study, the SI internal‐external motion is well correlated, with small time shifts and corresponding amplitude mismatches. Although the AP internal‐external motion reveals larger time shifts than along the SI direction, the corresponding amplitude mismatches are below .
Off‐axis dose response characteristics of an amorphous silicon electronic portal imaging device
Authors: Greer Peter B.
Published: October 2007

Amorphous silicon electronic portal imaging devices (EPIDs) have typically been calibrated to dose at central axis (CAX). Division of acquired images by the flood‐field (FF) image that corrects for pixel sensitivity variation as well as open field energy‐dependent off‐axis response variation should result in a flat EPID response over the entire matrix for the same field size. While the beam profile can be reintroduced to the image by an additional correction matrix, the CAX EPID response to dose calibration factor is assumed to apply to all pixels in the detector. The aim of this work was to investigate the dose response of the Varian aS500 amorphous silicon detector across the entire detector area. First it was established that the EPID response across the panel became stable (within ) for MU settings greater than . The EPID was then FF calibrated with a high MU setting of for all subsequent experiments. Whole detector images with varying MU settings from 2–500 were then acquired for two dose rates (300 and ) for photons for two EPIDs. The FF corrected EPID response was approximately flat or uniform across the detector for greater than delivered (within 0.5%). However, the off‐axis EPID response was greater than the CAX response for small MU irradiations, giving a raised EPID profile. Up to 5% increase in response at off‐axis compared to CAX was found for very small MU settings for one EPID, while it was within 2% for the second (newer) EPID. Off‐axis response nonuniformities attributed to detector damage were also found for the older EPID. Similar results were obtained with the EPID at energy and operating in asynchronous mode (acquisition not synchronized with beam pulses), however the profiles were flatter and more irregular for the small MU irradiations. By moving the detector laterally and repeating the experiments, the increase in response off‐axis was found to depend on the pixel position relative to the beam CAX. When the beam was heavily filtered by a phantom the off‐axis response variation was reduced markedly to within 0.5% for all MU settings. Independent measurements of off‐axis point doses with ion chamber did not show any change in off‐axis factor with MUs. Measurements of beam quality for MU settings of 2, 5, and 100 at central axis and at off‐axis could not explain the effect. The response change is unlikely to be significant for clinical IMRT verification with this imaging/acclerator system where MUs are of the order of 100–300, provided the detector does not exhibit radiation damage artifacts.
Automated contour mapping using sparse volume sampling for 4D radiation therapy
Authors: Chao Ming , Schreibmann Eduard , Li Tianfang , Wink Nicole , Xing Lei
Published: October 2007

The purpose of this work is to develop a novel strategy to automatically map organ contours from one phase of respiration to all other phases on a four‐dimensional computed tomography (4D CT). A region of interest (ROI) was manually delineated by a physician on one phase specific image set of a 4D CT. A number of cubic control volumes of the size of were automatically placed along the contours. The control volumes were then collectively mapped to the next phase using a rigid transformation. To accommodate organ deformation, a model‐based adaptation of the control volume positions was followed after the rigid mapping procedure. This further adjustment of control volume positions was performed by minimizing an energy function which balances the tendency for the control volumes to move to their correspondences with the desire to maintain similar image features and shape integrity of the contour. The mapped ROI surface was then constructed based on the central positions of the control volumes using a triangulated surface construction technique. The proposed technique was assessed using a digital phantom and 4D CT images of three lung patients. Our digital phantom study data indicated that a spatial accuracy better than 2.5 mm is achievable using the proposed technique. The patient study showed a similar level of accuracy. In addition, the computational speed of our algorithm was significantly improved as compared with a conventional deformable registration‐based contour mapping technique. The robustness and accuracy of this approach make it a valuable tool for the efficient use of the available spatial‐tempo information for 4D simulation and treatment.
DEVELOPMENT OF COMPUTATIONAL METHODOLOGIES FOR THE PREDICTION AND ANALYSIS OF SOLID-STATE TERAHERTZ SPECTRA
Authors: Allis Damian G. , Korter Timothy M.
Published: October 2007

The analytical applications of terahertz (THz) spectroscopy for the characterization of molecular solids have been limited by the lack of information concerning the assignment of observed spectral features to specific internal (intramolecular) and external (intermolecular) atomic motions. Computational methodologies addressing the assignment of spectral data are the enabling technology for moving THz spectroscopy to the forefront of available detection methods for both imaging and spectroscopic applications. Solid-state density functional theory (DFT) studies have been performed on the high explosives cyclotetramethylenetetranitramine (HMX) and pentaerythritol tetranitrate (PETN) in order to address the dependencies of the predictions of solid-state vibrations in the terahertz (3 to 120 cm−1) region on the choice of basis set and integration grid size, building on previous work that examined this dependency on the choice of density functional. DFT THz simulations reveal that both the choice of basis set and grid size have important influences on the reproduction of spectral features. The sensitivity to basis set choice is most pronounced in the calculation of vibrational intensities, where it is found that THz absorption intensities are most accurately reproduced when derived from basis set-sensitive Mulliken atomic charges as opposed to basis set-insensitive atomic charges generated by the Hirshfeld partitioning method.
AN ANALYSIS OF THE THZ FREQUENCY SIGNATURES IN THE CELLULAR COMPONENTS OF BIOLOGICAL AGENTS
Authors: BYKHOVSKI ALEXEI , GLOBUS TATIANA , KHROMOVA TATYANA , GELMONT BORIS , WOOLARD DWIGHT
Published: October 2007

The development of an effective biological (bio) agent detection capability based upon terahertz (THz) frequency absorption spectra will require insight into how the constituent cellular components contribute to the overall THz signature. In this work, the specific contribution of ribonucleic acid (RNA) to THz spectra is analyzed in detail. Previously, it has only been possible to simulate partial fragments of the RNA (or DNA) structures due to the excessive computational demands. For the first time, the molecular structure of the entire transfer RNA (tRNA) molecule of E. coli was simulated and the associated THz signature was derived theoretically. The tRNA that binds amino acid tyrosine (tRNAtyr) was studied. Here, the molecular structure was optimized using the potential energy minimization and molecular dynamical (MD) simulations. Solvation effects (water molecules) were also included explicitly in the MD simulations. To verify that realistic molecular signatures were simulated, a parallel experimental study of tRNAs of E. coli was also conducted. Two very similar molecules, valine and tyrosine tRNA were investigated experimentally. Samples were prepared in the form of water solutions with the concentrations in the range 0.01-1 mg/ml. A strong correlation of the measured THz signatures associated with valine tRNA and tyrosine tRNA was observed. These findings are consistent with the structural similarity of the two tRNAs. The calculated THz signature of the tyrosine tRNA of E. coli reproduces many features of our measured spectra, and, therefore, provides valuable new insights into bio-agent detection.
STANDOFF SENSING AND IMAGING OF EXPLOSIVE RELATED CHEMICAL AND BIO-CHEMICAL MATERIALS USING THz-TDS
Authors: Zhong Hua , Redo-Sanchez Albert , Zhang Xi-Cheng
Published: October 2007

We report the sensing and imaging of explosive related chemical and bio-chemical materials by using terahertz time domain spectroscopy (THz-TDS) at standoff distance. The 0.82 THz absorption peak of RDX is observed at a distance up to 30 m away from the emitter and receiver. Multiple absorption features of RDX, 2,4-DNT and Glutamic Acid are identified by using a large scale 2-D imaging system. These results support the feasibility of using THz-TDS technique in remote sensing and detection of chemical materials.
AMBIENT AIR USED AS THE NONLINEAR MEDIA FOR THZ WAVE GENERATION
Authors: Xie Xu , Dai Jianming , Yamaguchi Masashi , Zhang X. -C.
Published: October 2007

We report the first systematic study of broadband THz wave generation with ambient air as the nonlinear media. Generation of pulsed THz waves with mixing the fundamental and the second harmonic beams in air has been previously demonstrated by Cook et al. and Hartmut et al. while different groups obtained different results. To verify the proposed mechanism of strong THz wave generation, we measured dependence of generated THz field on the polarization, amplitude and phase of the individually controlled two beams. Our results confirm that four-wave-mixing rectification is the major mechanism this phenomenon, and the amplitude and polarity of generated THz wave can be controlled by the relative phase of the beams. This work is significant by providing the feasibility of THz wave generation and detection with a standoff distance greater than 50 meters.
TIME DOMAIN TERAHERTZ IMAGING OF THREATS IN LUGGAGE AND PERSONNEL
Authors: ZIMDARS DAVID , WHITE JEFFREY , STUK G. , SUCHA G. , FICHTER G. , WILLIAMSON S. L.
Published: October 2007

We demonstrate a large area time domain terahertz (THz) imaging system capable of scanning 1 meter square area in less than 20-100 minutes for several security applications. The detection of concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); and flammables in luggage, packages and personnel has been demonstrated. Transmission mode images of luggage containing threat items are discussed. Reflection mode images of luggage and personnel are discussed. Time domain THz images can be analyzed for 3 dimensional and volumetric information. Time domain THz images have advantages over coherent narrow band imaging methods, with freedom from interference artifacts and with greater ability to discard irrelevant or intervening reflections through time discrimination.
EXPERIMENTAL AND DENSITY FUNCTIONAL THEORY STUDY ON THz SPECTRA OF 4-NT AND 2, 6-DNT
Authors: CHEN YUNQING , LIU HAIBO , ZHANG X. -C.
Published: October 2007

Terahertz (THz) spectra of two TNT-related compounds (4-NT and 2, 6-DNT) are investigated using Fourier transform infrared spectroscopy (FTIR, 1.5-20 THz) and THz time-domain spectroscopy (THz-TDS, 0.2-2.5 THz). Density functional theory (DFT) is applied to calculate THz spectra of these two compounds. Transmission, diffuse reflection, and calculated spectra are in good agreement. The measured THz resonance lines from the transmission and diffuse reflectance spectra are assigned based on the DFT simulation. The observed THz signatures imply that THz spectrum has potential for standoff detection of explosives and related compounds (ERCs) in the THz range.
INTERACTIONS OF THz VIBRATIONAL MODES WITH CHARGE CARRIERS IN DNA: POLARON-PHONON INTERACTIONS
Authors: RAMADURAI DINAKAR , YAMANAKA TAKAYUKI , LI YANG , VASUDEV MILANA , SANKAR VISWANATH , DUTTA MITRA , STROSCIO MICHAEL A. , RAJH TIJANA , SAPONJIC ZORAN
Published: October 2007

This paper presents models and experimental measurements that shed light on THz-phonon mediated transport of polarons in biomolecules. Polaron transport in DNA has been considered recently in view of the expected derealization of charge carriers on a one-dimensional wire as well as the highly charged nature of DNA.1,2 An understanding of the electrical transport properties and THz-phonon interactions of biomolecules is important in view of DNA's potential applications both as electrically conductive wires and as structures that facilitate the chemically-directed assembly of massively integrated ensembles of nanoscale semiconducting elements into terascale integrated networks. Moreover, understanding these interactions provides information of the THz spectrum of vibrational modes in DNA. A primary focus of this paper is on charge transport in biomolecules using indirect-bandgap colloidal nanocrystals linked with biomolecules.3 Through a combination of theoretical and experimental approaches,4-7 this paper focuses on understanding the electrical properties and THz-frequency interactions of DNA. Moreover, this paper presents observed charge transport phenomena in DNA and discusses how these measurements are related to carrier scattering from the THz vibrational modes in DNA. Indeed, carrier transport in DNA is analyzed in light of theoretical calculations of the effects of THz-frequency phonon emission by propagating carriers, THz-frequency phonon absorption by propagating and trapped carriers, and effective mass calculations for specific sequences of the DNA bases.1-7 These studies focus on THz-phonon-mediated processes since an extra carrier on a one-dimensional chain minimizes its energy by forming an extended polaron, and since many biomolecules, including DNA, exhibit THz vibrational spectra.8 Accordingly, these calculations focus on THz-phonon-mediated processes. These results are discussed in terms of the role of THz-phonon-mediated charge trapping and detrapping effects near guanine-rich regions of the DNA as well as on the understanding and identification of DNA with specific base sequences that promote charge transport. As in previous studies, optical excitation is used to inject carriers into DNA wires. Moreover, this paper reports on the use of gel electrophoresis to study charge-induced cleavage of DNA and the related transport of charge in DNA. Phonon absorption and emission from polarons in DNA,9 is analyzed using parameters from the well-known Su-Schrieffer-Heeger Hamiltonian.
AN OPTICALLY-TRIGGERED I-RTD HYBRID THz OSCILLATOR DESIGN
Authors: WOOLARD DWIGHT , ZHANG WEIDONG , BROWN ELLIOTT , GELMONT BORIS , TREW ROBERT
Published: October 2007

A design and analysis study is presented for a new optically-triggered (OT) interband resonant-tunneling-diode (I-RTD) device that has potential for generating terahertz (THz) frequency oscillations and achieving enhanced output power levels under pulsed operation. The proposed device utilizes novel nanoscale mechanisms to achieve externally driven oscillations that consist of two phases – i.e., an initial transient phase produced by a natural Zener (interband) tunneling process and a second discharging transient phase induced by optical annihilation of stored hole-charge by externally-injected photon flux. The specific focus of this paper will be on an OT-I-RTD oscillator that utilizes In 1- x Ga x As / GaSb y As 1- y hetero-systems and the application of band-engineering to enable triggering by 1.55 μm laser technology. The paper presents performance results for the hybrid circuit design, along with a practical implementation strategy for integrating the optical triggering and an analysis of the heating induced during large signal operation.
TERAHERTZ PHONON-POLARITON IMAGING FOR THE APPLICATION OF CHEMICAL DETECTION
Authors: Yamaguchi Masashi , Wang Minfeng , Suarez Pablo
Published: October 2007

A combination of Terahertz (THz) polariton spectroscopy and polariton imaging technique for the application to chemical sensing is presented. We use phonon-polaritons, a coupled oscillation of the lattice vibration and radiation field, as an intense radiation source for THz spectroscopy. The propagation process of the polaritons generated in one of the two LiNbO 3 transducer crystals through the sample sandwiched between the crystals is visualized using a polariton imaging technique. Partially reflected polaritons at the transducer-sample interface and polaritons partially transmitted through the sample are visualized simultaneously in a single frame of an image. The temporal profile of reflected and transmitted phonon-polaritons can be obtained without scanning the delay time between the pump and probe femtosecond laser pulses unlike THz time-domain spectroscopy which requires point-by-point acquisition of the temporal pulse profile using conventional pump-probe scheme. The results suggest possible application of this technique to the chemical sensing with fast acquisition rate. The technique has been successfully applied to the measurement of liquid and solid samples, and simultaneous measurement of multiple samples has also been achieved.
NEW TECHNIQUE TO SUPPRESS SIDELOBE CLUTTER IN PERIMETER SECURITY SYSTEMS
Authors: WEBB G. W. , MININ I. V. , MININ O. V.
Published: October 2007

False echoes degrade the operation of radar and imaging antennas. The false returns or clutter arise from antenna sidelobes and raise the threshold of detection in perimeter security systems. Accordingly there is great interest in reducing the sidelobes in present day millimeter wave and future terahertz antennas. Here we describe a new technique to suppress antenna sidelobe returns. The technique exploits our ability to distinguish between the phase of desired signals arriving in the antenna main beam and the phase of undesired clutter signals coming from the sidelobes. We demonstrate that through modulation of phase and taking the Fourier transform of the received signal, we can preferentially suppress the clutter return relative to the desired main beam signal. Suppression of average clutter return of over 25 dB is found.
MILLIMETER AND SUB-MILLIMETER WAVE PERFORMANCE OF AN ERAS:INALGAAS SCHOTTKY DIODE COUPLED TO A SINGLE-TURN SQUARE SPIRAL
Authors: Brown E. R. , Young A. C. , Bjarnason J. E. , Zimmerman J. D. , Gossard A. C. , Kazemi H.
Published: October 2007

We report the first experimental results for noise-equivalent power (NEP) and noise-equivalent temperature difference (NETD) of single-crystal ErAs:InAlGaAs , zero-bias rectifier diodes coupled to free space quasi-optically in the THz region. At a frequency of 639 GHz, an optical NEP of 4.0×10−12 W / Hz 1/2 is measured with the rectifier coupled to a quasi-plane-wave coherent source through a single-turn square spiral antenna. With a broadband thermal (hot water) source, an NETD of 120 mK is measured from the same device. Antenna radiation patterns at 100 GHz and 639 GHz are also presented.
LONG-WAVE INFRARED AND TERAHERTZ-FREQUENCY LASING BASED ON SEMICONDUCTOR NANOCRYSTALS
Authors: RUPASOV VALERY I. , KRIVOSHLYKOV SERGEI G.
Published: October 2007

ALTAIR Center develops long-wave infrared (LWIR) and terahertz-frequency (THz) lasers operating at room temperature employing intraband luminescence in colloidal semiconductor nanocrystals, in which the optical transition frequencies can be easily tuned to the desired values by an appropriate choice of the semiconductor material and radius of the nanocrystals.
SYNCHRONIZATION AND ANTI-SYNCHRONIZATION OF CHAOTIC SYSTEMS BASED ON LINEAR SEPARATION AND APPLICATIONS IN SECURITY COMMUNICATION
Authors: WANG XINGYUAN , WANG JIAGANG
Published: October 2007

This paper analyzes a coupled dynamic system. Based on the stability criterion of linear systems, a new approach for constructing chaotic synchronization and anti-synchronization is proposed. The complete synchronizations and anti-synchronizations of the coupled dynamic system are achieved via the linear separation method. Finally, the method is applied in security communication. Numerical simulations are provided for illustration and verification of the proposed method.
THE FIDELITY OF GENERAL BOSONIC CHANNELS WITH PURE STATE INPUT
Authors: ZHAO MEISHENG , QIN TAO , ZHANG YONGDE
Published: October 2007

We give the exact form of the fidelity for general bosonic Gaussian channels in cases where the channel's input are limited to Gaussian pure states. Some examples have been studied and the properties of the fidelity for memory channel are carefully examined.
TRICRITICAL BEHAVIOR AT THE SMECTIC-A-SMECTIC-${\rm C}^{*}_{\alpha}$ PHASE TRANSITION
Authors: MUKHERJEE PRABIR K.
Published: October 2007

A simple phenomenological approach to the description of the electric field effect on the Smectic-A-Smectic-[Formula: see text] phase is discussed. It is shown that with a particular value of the electric field E tcp the second-order Smectic-A-Smectic-[Formula: see text] phase transition (no field) becomes first order at a tricritical point. The results are in good agreement with recent experiments.
ELECTRICAL EXPRESSION OF SPIN ACCUMULATION IN FERROMAGNET/SEMICONDUCTOR STRUCTURES
Authors: CYWIŃSKI ŁUKASZ , DERY HANAN , DALAL PARIN , SHAM L. J.
Published: October 2007

We treat the spin injection and extraction via a ferromagnetic metal/semiconductor Schottky barrier as a quantum scattering problem. This enables the theory to explain a number of phenomena involving spin-dependent current through the Schottky barrier, especially the counter-intuitive spin polarization direction in the semiconductor due to current extraction seen in recent experiments. A possible explanation of this phenomenon involves taking into account the spin-dependent inelastic scattering via the bound states in the interface region. The quantum-mechanical treatment of spin transport through the interface is coupled with the semiclassical description of transport in the adjoining media, in which we take into account the in-plane spin diffusion along the interface in the planar geometry used in experiments. The theory forms the basis of the calculation of spin-dependent current flow in multi-terminal systems, consisting of a semiconductor channel with many ferromagnetic contacts attached, in which the spin accumulation created by spin injection/extraction can be efficiently sensed by electrical means. A three-terminal system can be used as a magnetic memory cell with the bit of information encoded in the magnetization of one of the contacts. Using five terminals we construct a reprogrammable logic gate, in which the logic inputs and the functionality are encoded in magnetizations of the four terminals, while the current out of the fifth one gives a result of the operation.
THE AGING BEHAVIOR OF THE RANDOM n-VECTOR MODEL WITH LONG-RANGE INTERACTION
Authors: CHEN YUAN
Published: October 2007

The aging behavior of the random n-vector model with long-range interaction decaying as r-(d+σ) (where d is the dimensionality), is investigated by the theoretic renormalization-group approach. The system initially disordered at a high temperature is firstly quenched to the critical temperature T c and then released to an evolution with model A dynamics. The aging properties are studied by the short-time expansions. The scaling behavior of two-time response and correlation functions are obtained in a frame of the expansion in ∊ = 2σ-d. In dimensions d < 2σ, the long-time limit of the critical fluctuation dissipation ratio X∞ is calculated up to one-loop order. The simulation of X∞ is discussed.
Role of CYP1B1 in Glaucoma
Authors: Vasiliou Vasilis , Gonzalez Frank J.
Published: October 2007

Glaucoma is a leading cause of blindness, estimated to affect 60 million people by 2010, and represents a heterogeneous group of neurodegenerative disease. The two major types of glaucoma include primary open-angle glaucoma (POAG) and primary congenital glaucoma (PCG). A genetically heterogeneous group of developmental disorders known as anterior segment dysgenesis (ASD) have been reported to be associated with increased intraocular pressure (IOP) and glaucoma. These include Peters’ anomaly, Rieger's anomaly, aniridia, iris hypoplasia, and iridogoniodysgenesis. Genetic linkage analysis and mutation studies have identified CYP1B1 as a causative gene in PCG, as a modifier gene in POAG, and, on rare occasions, as causative gene in POAG as well as in several ASD disorders. CYP1B1-deficient mice exhibit abnormalities in their ocular drainage structure and trabecular meshwork that are similar to those reported in human PCG patients. Accordingly, it is speculated that diminished or absent metabolism of key endogenous CYP1B1 substrates adversely affects the development of the trabecular meshwork. CYP1B1 protein is involved in the metabolism of steroids, retinol and retinal, arachidonate, and melatonin. The conserved expression of CYP1B1 in both murine and human eyes, its higher expression in fetal than adult eyes, and its biochemical properties are consistent with this hypothesis. The exact role of CYP1B1 in the pathogenesis of glaucoma and other ASD disorders remains to be elucidated.
Mechanism-Based Concepts of Size and Maturity in Pharmacokinetics
Authors: Anderson B.J. , Holford N.H.G.
Published: October 2007

Growth and development can be investigated using readily observable demographic factors such as weight and age. Size is the primary covariate and can be referenced to a 70-kg person with allometry using a coefficient of 0.75 for clearance and 1 for volume. The use of these coefficients is supported by fractal geometric concepts and observations from diverse areas in biology. Fat free mass (FFM) might be expected to do better than total body weight when there are wide variations in fat affecting body composition. Clearance pathways develop in the fetus before birth. The use of postnatal age as a descriptor of maturation is unsatisfactory because birth may occur prematurely; therefore postmenstrual age is a superior predictor of elimination function. A sigmoid Emaxmodel (Hill equation) describes gradual maturation of clearance in early life leading to a mature adult clearance achieved at a later age.
Ecologic Studies Revisited
Authors: Wakefield Jonathan
Published: October 2007

Ecologic studies use data aggregated over groups rather than data on individuals. Such studies are popular because they use existing databases and can offer large exposure variation if the data arise from broad geographical areas. Unfortunately, the aggregation of data that define ecologic studies results in an information loss that can lead to ecologic bias. Specifically, ecologic bias arises from the inability of ecologic data to characterize within-area variability in exposures and confounders. We describe in detail particular forms of ecologic bias so that their potential impact on any particular study may be assessed. The only way to overcome such bias, while avoiding uncheckable assumptions concerning the missing information, is to supplement the ecologic with individual-level information, and we outline a number of proposals that may achieve this aim.
Protective Interventions to Prevent Aflatoxin-Induced Carcinogenesis in Developing Countries
Authors: Groopman John D. , Kensler Thomas W. , Wild Christopher P.
Published: October 2007

The public health impact of aflatoxin exposure is pervasive in economically developing countries; consequently, we need to design intervention strategies for prevention that are practicable for these high-risk populations. The adverse health consequences of aflatoxins in populations are quite varied, eliciting acute effects, such as rapid death, and chronic outcomes, such as hepatocellular carcinoma. Furthermore, a number of epidemiological studies describe a variety of general adverse health effects associated with aflatoxin, such as impaired growth in children. Thus, the magnitude of the problem is disseminated across the entire spectrum of age, gender, and health status in the population. The aflatoxins multiplicatively increase the risk of liver cancer in people chronically infected with hepatitis B virus (HBV), which illustrates the deleterious impact that even low toxin levels in the diet can pose for human health. Thus other aflatoxin interactions, which likely contribute to the diesease burden, still remain to be identified. Therefore, many diverse and appropriate strategies for disease prevention are needed to decrease the incidence of aflatoxin carcinogenesis in developing countries.