Exploration of a double-tapered disc-loaded circular waveguide for a wideband gyro-TWT

The analysis of a disc-loaded circular waveguide interaction structure of a gyro-traveling-wave-tube (gyro-TWT) considering standing and propagating mode harmonics in the disc-occupied and disc-free regions, respectively, gave the beam-absent dispersion relation of the waveguide. The axial phase propagation constant predicted by the dispersion relation was substituted into the gyro-TWT gain-equation, the latter obtainable from the beam-present dispersion relation of the device. A method of double-tapering the structure dimensions was proposed that consists in tapering the disc-hole radius to distribute the midband frequency of amplification over a wide range of frequencies, and simultaneously tapering the waveguide-wall radius to compensate for gain reduction at band edges due to disc-hole radius tapering. The method has demonstrated wide device bandwidths at relatively large gain values.     

Parameters to Define the Electron Beam Trajectory of a Double-Tapered Disc-Loaded Wideband Gyro-TWT in Profiled Magnetic Field

In the method of tapering the cross section of the interaction structure for broadbanding a gyro-TWT, the different portions of the interaction length of the tapered-cross-section waveguide become effective for different frequency ranges if the magnetic field and beam parameters are profiled to maintain the condition of electron cyclotron resonance throughout the interaction length. In the present paper, the study of profiling the magnetic field and beam parameters in steps of the stepped analytical model of a double-tapered disc-loaded circular waveguide was made throughout the steps of the model. In the observed profile, the magnetic flux density in a typical step relative to its value in first-step decreases from first-step (gun-end) to end-step (collector-end) of the model considering the up-tapering schemes, in which structure parameters increase from gun-end to collector-end. Also, the transverse beam velocity in a typical step relative to its value in first-step decreases from gun-end to collector-end. However, the Larmor radius in a typical step relative to its value in first-step as well as the hollow-beam radius in a typical step relative to its value in first-step, both increase from gun-end to collector-end in the model considering the up-tapering schemes.     

Performance evaluation of breast lesion detection systems with expert delineations: a comparative investigation on mammographic images

Multimedia Tools and Applications - Performance of computerized diagnostic systems yearning to be approved by medical regulatory bodies must meet the expectations of human experts. Highly accurate...     

Spontaneous programmed cell death in infiltrating duct carcinoma: association with p53, BCL-2, hormone receptors and tumor proliferation

Recent evidence has emphasized the importance of programmed cell death or apoptosis in the maintenance of tissue homeostasis and pathogenesis of tumors. This study, analyzed in breast cancer, investigates the significance of apoptosis in relation to the expression of p53 and bcl-2 proteins, tissue proliferation defined by Ki-67 expression, hormone receptors and tumor grade. The extent of apoptosis was defined by morphological criteria and the TUNEL (Tdt-mediated dUTP biotin nick end labelling) assay. Immunocytochemistry was performed for p53, bcl-2, estrogen receptor, progesterone receptor and Ki-67 expression. Mutant p53 protein was detected using a mutant specific ELISA. Immunoreactivity of p53 significantly correlated with the presence of mutant p53 protein detected by ELISA (r = 0.654, p = 0.00001). An inverse correlation was observed between bcl-2 expression and the extent of apoptosis (r = -0.33369, p = 0.01912). The extent of apoptosis directly correlated with p53 protein accumulation (r = 0.485, p = 0.00041), Ki-67 immunoreactivity (r = 0.435, p = 0.001), histopathological grade (r = 0.492, p = 0.0003), tumor size (r = 0.326, p = 0.023) and lymph node status (r = 0.287, p = 0.047). A direct correlation was also observed between p53 expression and Ki-67 immunoreactivity (r = 0.623, p = 0.0002). There was no statistically significant association between estrogen and progesterone receptor status and apoptosis. In addition, the TNM stage of the disease correlated with immunoreactivity of p53 (r = 0.572, p = 0.00012) and Ki-67 (r = 0.3744, p = 0.00818). Bcl-2, by inhibiting apoptosis, may cause a shift in tissue kinetics towards the preservation of genetically aberrant cells, thereby facilitating tumor progression. These results imply that rapidly proliferating tumors appear to have a high "cell turnover state" in which there may be an increased chance of apoptosis amongst the proliferating cells. The ability of apoptosis to also occur in the presence of mutant p53 protein suggests the existence of at least two p53-dependent apoptotic pathways, one requiring activation of specific target genes and the other independent of it.     

Diffraction of elastic sphericalP waves by a cylindrical cavity

Summary This paper deals with the three dimensional diffraction of impulsive compressional waves by a cylindrical cavity. The cavity is embedded in an unbounded, isotropic, homogeneous elastic medium. The compressional point source, generating the incident pulse, is supposed to be situated outside the cavity. The formal solution to the problem is obtained in integral form. The integrals are evaluated asymptotically for the early time motion by the residue-Cagniard method.With 6 Figures     

Transfectable and transplantable postmitotic human neurons: a potential "platform" for gene therapy of nervous system diseases

OBJECTIVE: To evaluate F-18 fluorodeoxyglucose positron emission tomography (PET) in terms of its sensitivity and specificity in diagnosing malignant pulmonary nodules and staging bronchogenic carcinoma. METHODS: A retrospective review of any patient that presented to the VA Palo Alto Health Care System with a pulmonary nodule between 9/94 and 3/96 revealed 49 patients (four female, 45 male) age 37-85 (mean 63) with 54 pulmonary nodules who had: chest CT scan, PET scan; and tissue characterization of the nodule. Characterization of each nodule was achieved by histopathologic (N = 44) or cytopathologic (N = 10) analysis. Of the 49 patients, 18 had bronchogenic carcinoma which was adequately staged. Mediastinal PET and CT findings in these 18 patients were compared with the surgical pathology results. N2 disease was defined as mediastinal lymph node involvement by the American Thoracic Society's classification system. Mediastinal lymph nodes were interpreted as positive by CT if they were larger that 1.0 cm in the short-axis diameter. RESULTS: Sensitivity and specificity for the diagnosis of malignant pulmonary nodules using PET was 93 and 70%, respectively. All nodules (N = 3) that were falsely positive by PET scan were infectious in origin. All nodules (N = 4) that were falsely negative by PET were technically limited studies (outdated scanner, no attenuation correction, hyperglycemia) except for one case of metastatic adenocarcinoma. The sensitivity and specificity of PET in diagnosing N2 disease was 67 and 100%, compared with 56% and 100% for CT scan (not statistically significant). However, one more patient with N2 disease was correctly diagnosed by PET than by CT scan. CONCLUSION: PET is a valuable tool in the diagnosis and management of pulmonary nodules and may more accurately stage patients with bronchogenic carcinoma than CT scanning alone.     

Corrosion studies on pulsed and direct current chromium deposits

Chromium was deposited on steel substrates using direct current pulsed high frequency and pulsed low frequency plating methods. The samples obtained from the different plating techniques were later exposed to a corrosive NaCl solution. The time of exposure was varied, for 0, 80 and 140 hours and later the samples were subjected to impedance measurements. In the present study an attempt has been made to characterise the best plating method using impedance data analysis.     

Segmentation of malignant tumours in mammogram images: A hybrid approach using convolutional neural networks and connected component analysis

The segmentation of breast lesions is an important step in the computer-aided analysis of the mammogram. The presence of noise in mammograms makes lesion detection challenging particularly for complex malignant lesions. Pre-processing techniques can deal with the noise issue but distorts the important shape features. This motivates us to propose a novel hybrid approach by combining a convolution neural network (CNN) with connected component analysis (CCA) to segment malignant breast lesions without any pre-processing to avoid any distortion in image sharpness at the initial stages. Two well-known segmentation techniques namely, K-means (KM) and Fuzzy c-means (FCM) are also used to compare the results. From a pool of 1045 mammographic cancer images acquired from the Digital Database for Screening Mammography (DDSM), 1016 are used for training and validation, and 29 are used for testing. All three results (Hybrid, KM and FCM) are compared against the results by the expert Radiologist. The results indicate that, among various segmentation techniques, the proposed hybrid approach achieves the highest accuracy (90%), Matthew's correlation coefficient (0.79), Jaccard index (0.73) and the Dice similarity coefficient (0.84). Other performance evaluation techniques such as; precision, sensitivity, specificity, false-positive rate, false discovery rate, negative predictive value and false-negative rate also show the superior performance of the proposed hybrid approach. Statistical analysis (Mann–Whitney U test, T-test, Chi-square test, Kolmogorov–Smirnov test and Wilcoxon test), graphical analysis (Regression and Bland–Altman plots) and receiver operating characteristic curve further demonstrate the stability and consistency of the results.     

Recovery of Drug Delivery Nanoparticles from Human Plasma Using an Electrokinetic Platform Technology

The effect of complex biological fluids on the surface and structure of nanoparticles is a rapidly expanding field of study. One of the challenges holding back this research is the difficulty of recovering therapeutic nanoparticles from biological samples due to their small size, low density, and stealth surface coatings. Here, the first demonstration of the recovery and analysis of drug delivery nanoparticles from undiluted human plasma samples through the use of a new electrokinetic platform technology is presented. The particles are recovered from plasma through a dielectrophoresis separation force that is created by innate differences in the dielectric properties between the unaltered nanoparticles and the surrounding plasma. It is shown that this can be applied to a wide range of drug delivery nanoparticles of different morphologies and materials, including low‐density nanoliposomes. These recovered particles can then be analyzed using different methods including scanning electron microscopy to monitor surface and structural changes that result from plasma exposure. This new recovery technique can be broadly applied to the recovery of nanoparticles from high conductance fluids in a wide range of applications.