Design and characterization of third-order Sallen-Key digital filter in nuclear signal processing.

The Gaussian filter shaping circuit is widely used in the nuclear pulse signal processing due to its good performance in amplitude extraction and pulse counting. A third-order Sallen-Key (3rd S-K) filter shaping circuit is designed based on a RC integrator and a second-order Sallen-Key (2nd S-K) circuit. According to the digital 3rd S-K, the transfer functions is derived in the Laplacian domain, and the numerical recurrence model is analyzed and researched, the purpose is to obtain its transfer function and amplitude-frequency response curve in the z-domain. For the simulation and actual sampling of the nuclear signal, digital shaping processing is performed at different parameters, three parameters (d, SNR, δ) are defined to compare and analyze the amplitude extraction, noise suppression and symmetry of the digital shaping method, which shows that as the shaping parameters increases, the digital shaping output noise suppression performance is better, the SNR increased from 49.25 to 64.21, the waveform is more symmetrical, the δ reduced from 34.05 to 0.22. At the same parameters, it is compared and analyzed with CR-RC3 and 2nd S-K shaping methods, according to the digital Gaussian shaping results, the 3rd S-K digital shaping method has better pulse amplitude extraction(d = 36.06%), noise suppression performance (SNR = 64.21) and waveform symmetry (δ = 0.22). Under different shaping methods, the energy resolution and pulse counting rate of the Fe characteristic X-ray energy spectrum are compared based on a Si-PIN detector. The results show that the 3rd S-K digital shaping method has better energy resolution performance and comprehensive performance indicators, which can be further applied for digital shaping of nuclear pulse signals.

Ultrastructural study of closed macular hole- preliminary application of a novel high magnification module combining with OCT.

BACKGROUND: As a novel high magnification module (HMM) combining with OCT (OCT-HMM) is able to detect the microstructure of retina, we apply it to explore the ultrastructure of the macula after closure of the idiopathic macular hole (IMH) by surgery. METHODS: This is an observational case series study in which patients with full-thickness IMHs who had undergone successful macular closure by vitrectomy and internal limiting membrane peeling and healthy subjects were recruited. After comprehensive ophthalmic examinations, the images of macular area were obtained and collected by professional operators using OCT-HMM. Then images were independently analyzed by 4 masked vitreoretinal specialists. RESULTS: A total of 24 IMH eyes and 42 healthy eyes were examined. HMM images were obtained in 10 IMH eyes. Among them, 4 eyes whose macula closed completely with recovery of photoreceptor layer presented a dark arc nasal to the fovea, oriented to the optic, and the notch of arc faced temporally. Six eyes in which the macula closed incompletely with photoreceptor cells loss revealed a dark ring with uneven bright spots inside. The other 14 eyes failed to obtain clear images by OCT-HMM. The contra lateral eyes of the patients and the healthy subjects' eyes succeeded to obtain the HMM images which displayed evenly grey background thickly covered with tiny bright dots that was in similar size and evenly and widely distributed and there no dark arc or ring. OCT B-scan and IR images could be acquired in all of the IMH and healthy eyes. CONCLUSION: The preliminary application of HMM has supplied us a brand-new insight into the microstructure of closed IMH. A dark arc sign could be detected with OCT-HMM in the macula which was functionally closed after surgery that was probably the healing mark on a microstructure photoreceptors level. Its existence and shape indicated that the functional closure followed by a retinal displacement mainly horizontally from temporal side to nasal side but not symmetric centripetally.

[Toxic effects of HSV-TK and CD-TK suicidal gene systems on prostate carcinoma cells].

BACKGROUND & OBJECTIVE: Suicidal gene therapy is one of promising gene therapies. In order to assess the value of suicidal gene therapy on human prostate carcinoma, the authors studied the toxic effects of HSV-TK gene and CD-TK fusion gene systems on prostate carcinoma cell line PC-3m. METHODS: HSV-TK gene and CD-TK fusion gene were separately transfected into PC-3m cells through retrovirus vectors. Reverse transcription-polymerase chain reaction (RT-PCR) was used to demonstrate successful transfection and transcription of suicidal genes. The toxic effects of GCV, 5-FC, and both of them on transfected PC-3m cells were explored by MTT assay; non-transfected PC-3m cells were used as control. RESULTS: Significantly cytotoxic activity of GCV was observed and 50% inhibitory concentration(IC(50)) was 8.34 microg/ml,the bystander effect of GCV was modest,while the bystander effect of 5-Fc was significant,it began to show when the percent of tansfected PC-3m cells in mixed cells was 5%. Simultaneous treatment with two prodrugs on CD-TK expressing cells resulted in additive or synergistic toxicity,coefficient of drug interaction(CDI) was under 1. CONCLUSION: CD-TK fusion suicidal gene system has significant toxic effect on PC-3m cells in vitro, which was superior to HSV-TK alone gene system.

Morphologies and phylogenetic classification of cellulolytic myxobacteria.

The evolutionary distances of the 16S rDNA sequences in cellulolytic myxobacteria are less than 3%, which units all the strains into a single genus, Sorangium. The size of myxospores and the shape of sporangioles, rather than fruiting body colors or swarm morphologies are consistent with the changes of the 16S rDNA sequences. It is suggested that there are at least two species in the genus Sorangium: one includes strains with small myxospores and spherical sporangioles, and the color of the fruiting bodies is normally orange or brown, though sometimes yellow or black. The second species has large myxospores, polyhedral sporangioles with many inter-cystic substrates, and normally deep brown to black color.