[An effective method for improving the imaging spatial resolution of terahertz time domain spectroscopy system].

Terahertz radiation is an electromagnetic radiation in the range between millimeter waves and far infrared. Due to its low energy and non-ionizing characters, THz pulse imaging emerges as a novel tool in many fields, such as material, chemical, biological medicine, and food safety. Limited spatial resolution is a significant restricting factor of terahertz imaging technology. Near field imaging method was proposed to improve the spatial resolution of terahertz system. Submillimeter scale's spauial resolution can be achieved if the income source size is smaller than the wawelength of the incoming source and the source is very close to the sample. But many changes were needed to the traditional terahertz time domain spectroscopy system, and it's very complex to analyze sample's physical parameters through the terahertz signal. A method of inserting a pinhole upstream to the sample was first proposed in this article to improve the spatial resolution of traditional terahertz time domain spectroscopy system. The measured spatial resolution of terahertz time domain spectroscopy system by knife edge method can achieve spatial resolution curves. The moving stage distance between 10 % and 90 Yo of the maximum signals respectively was defined as the, spatial resolution of the system. Imaging spatial resolution of traditional terahertz time domain spectroscopy system was improved dramatically after inserted a pinhole with diameter 0. 5 mm, 2 mm upstream to the sample. Experimental results show that the spatial resolution has been improved from 1. 276 mm to 0. 774 mm, with the increment about 39 %. Though this simple method, the spatial resolution of traditional terahertz time domain spectroscopy system was increased from millimeter scale to submillimeter scale. A pinhole with diameter 1 mm on a polyethylene plate was taken as sample, to terahertz imaging study. The traditional terahertz time domain spectroscopy system and pinhole inserted terahertz time domain spectroscopy system were applied in the imaging experiment respectively. The relative THz-power loss imaging of samples were use in this article. This method generally delivers the best signal to noise ratio in loss images, dispersion effects are cancelled. Terahertz imaging results show that the sample's boundary was more distinct after inserting the pinhole in front of, sample. The results also conform that inserting pinhole in front of sample can improve the imaging spatial resolution effectively. The theoretical analyses of the method which improve the spatial resolution by inserting a pinhole in front of sample were given in this article. The analyses also indicate that the smaller the pinhole size, the longer spatial coherence length of the system, the better spatial resolution of the system. At the same time the terahertz signal will be reduced accordingly. All the experimental results and theoretical analyses indicate that the method of inserting a pinhole in front of sample can improve the spatial resolution of traditional terahertz time domain spectroscopy system effectively, and it will further expand the application of terahertz imaging technology.

[Study of Terahertz Amplitude Imaging Based on the Mean Absorption].

A new method of terahertz (THz) imaging based on the mean absorption is proposed. Terahertz radiation is an electromagnetic radiation in the range between millimeter waves and far infrared. THz pulse imaging emerges as a novel tool in many fields because of its low energy and non-ionizing character, such as material, chemical, biological medicine and food safety. A character of THz imaging technique is it can get large amount of information. How to extract the useful parameter from the large amount of information and reconstruct sample's image is a key technology in THz imaging. Some efforts have been done for advanced visualization methods to extract the information of interest from the raw data. Both time domain and frequency domain visualization methods can be applied to extract information on the physical properties of samples from THz imaging raw data. The process of extracting useful parameter from raw data of the new method based on the mean absorption was given in this article. This method relates to the sample absorption and thickness, it delivers good signal to noise ratio in the images, and the dispersion effects are cancelled. A paper with a "THz" shape hole was taken as the sample to do the experiment. Traditional THz amplitude imaging methods in time domain and frequency domain are used to achieve the sample's image, such as relative reduction of pulse maximum imaging method, relative power loss imaging method, and relative power loss at specific frequency imaging method. The sample's information that reflected by these methods and the characteristics of these methods are discussed. The method base on the mean absorption within a certain frequency is also used to reconstruct sample's image. The experimental results show that this new method can well reflect the true information of the sample. And it can achieve a clearer image than the other traditional THz amplitude imaging methods. All the experimental results and theoretical analyses indicate that the method base on the mean absorption within a certain frequency can reflects sample absorb and thickness information, it can achieve good signal to noise ratio in the images. Because the absorption is mean absorption within in a certain frequency, so the method proposed in this article is especially suitable for samples with simple structure. And this new method can be a useful added tool for the other traditional THz amplitude imaging methods.

[THz time-domain spectroscopic study of composites filled with different carbon black].

Composites were prepared by filling high density polyethylene (HDPE) with acetylene black (AC-CB) and high-structure CB (HG-CB), respectively. Optical properties of the composites were characterized with terahertz time-domain spectroscopy (THz-TDS). It was found that as frequency increases the absorption coefficients of the composites increase whereas the refractive indexes decrease. Both the absorption coefficient and refractive index increase with increasing the particle concentration. The HG-CB filled composites have larger absorption coefficient but smaller refractive index compared with that of the AC-CB composites at the same particle concentration. These phenomena are related to the different particulate structures and aggregate structures of the CB particles. Assuming that the dielectric loss in THz frequency range is mainly attributed to the electron transport within the conductive clusters and the interfacial polarization of HDPE, the information of relaxation time and relaxation strength was obtained through fitting the experimental results to two-Debye theory of dipole relaxation.

[Qualitative and quantitative analyses of some saccharides by THz-TDS].

Terahertz (THz) radiation lies between the infrared and microwave range of the electromagnetic spectrum. Absorption spectrum in the THz range provides rich information about structure and weak interactions of biomolecules. THz absorption spectra of D-(-)-ribose, D-glucose, alpha-lactose monohydrate and beta-lactose were measured by terahertz time-domain spectroscopy (THz-TDS) in the frequency range of 0.3-1.6 THz at room temperature. The experimental results show that different saccharides have distinct THz absorption features, which suggests that THz-TDS is highly sensitive to molecular structures and components. Quantitative analysis of the mixtures of two to four saccharides was studied by linear regression with relative error less than 7.2%. The reasons for the relative error were discussed. The results demonstrate that THz-TDS is a promising and efficient method for both qualitative and quantitative analyses for pharmaceutical identification and biomolecular detection.

[Quantitative analysis of nucleotide mixtures with terahertz time domain spectroscopy].

Adenosine, thymidine, guanosine, cytidine and uridine form the building blocks of ribose nucleic acid (RNA) and deoxyribose nucleic acid (DNA). Nucleosides and their derivants are all have biological activities. Some of them can be used as medicine directly or as materials to synthesize other medicines. It is meaningful to detect the component and content in nucleosides mixtures. In the present paper, components and contents of the mixtures of adenosine, thymidine, guanosine, cytidine and uridine were analyzed. THz absorption spectra of pure nucleosides were set as standard spectra. The mixture's absorption spectra were analyzed by linear regression with non-negative constraint to identify the components and their relative content in the mixtures. The experimental and analyzing results show that it is simple and effective to get the components and their relative percentage in the mixtures by terahertz time domain spectroscopy with a relative error less than 10%. Component which is absent could be excluded exactly by this method, and the error sources were also analyzed. All the experiments and analysis confirms that this method is of no damage or contamination to the sample. This means that it will be a simple, effective and new method in biochemical materials analysis, which extends the application field of THz-TDS.

Molecular evidence of barley yellow dwarf virus replication/movement suppressed by the resistance gene Bdv2.

A wheat-Thinopyrum intermedium translocation line YW642 possesses the resistance to GAV serotype of barley yellow dwarf virus (BYDV), in which the resistance gene Bdv2 is derived from the chromosome 7X of Thinopyrum intermedium group 7. It is interesting to analyze BYDV accumulation content in the resistant and susceptible wheat plants for controlling BYDV disease and understanding the resistance mechanism against BYDV. In the paper, semi-quantitative reverse-transcription PCR (RT-PCR) was used to detect and quantify BYDV-GAV in the resistant and susceptible plants using specific primers for the coat protein (CP) and RNA-dependent RNA polymerase (RdRp) genes of BYDV-GAV serotype. On the inoculation site, the amount of the virus in the resistant wheat line (YW642) was much lower compared to the susceptible sib line (YW641). There was small amount of the virus could be detected in YW642 at 2-5 days post infestation (dpi), afterwards the amount of virus decreased and no virus could be detected at 14 and 16 dpi. In the uninoculated upper leaves, no BYDV was detected in YW642 from 1 to 14 dpi, while the virus could be detected at 3 dpi and then accumulated rapidly in YW641. These results showed at molecular level that the replication and/or movement of BYDV-GAV were strongly suppressed in YW642, presumably owing to the action of the BdV2 gene.

[Construction, characterization and screening of a transformation-competent artificial chromosome (TAC) library of wheat-Thinopyrum intermedium translocation line with resistance to barley yellow dwarf virus].

A transformation-competent artificial chromosome (TAC) library was constructed from the genomic DNA of wheat-Th. intermidium translocation line HW642 that harbor the barley yellow dwarf virus (BYDV) resistance gene derived from Th. intermidium. The library consists of 2.3 x 10(6) clones with an average insert size of 22kb, representing approximately 2.5 haploid genome equivalents and is able to give a greater than 95.77% probability of isolating single-copy DNA sequences from this library. The library was stored as frozen cultures in 24 96-well formats, each well containing approximately 1000 different clones. TAC clones containing interest gene could be identified by the pooled PCR technique. A sequence characterized amplified region (SCAR) marker cosegregated with BYDV resistance gene, derived from a simple sequence repeat (SSR) or microsatellite marker wms37 of wheat, was applied to screen the TAC library. Twelve clones were successfully selected by the pooled PCR method. PCR products were identified by hybridizing with the SCAR marker band of Th. intermidium. Out of 12 clones, 10 positive clones restricted by Hind III were shown to hybridize with genomic DNA of Th. intermidium. These results showed evidences that the 10 clones could be used as candidate clones for isolation of BYDV resistance and its related genes, and the TAC library is a useful resource for isolating genes.

[Development of new PCR markers specific to a Thinopyrum intermedium chromosome 2Ai-2 and cloning of the St-specific sequences].

To meet the need of selecting translocation lines, some new RAPD markers for 2Ai-2 chromosome of Th. intermedium were identified in the paper. Out of 320 RAPD primers, 2 specific primers, OPO05 and OPM04, can amplify respectively a specific band with size of about 650 bp and 1400 bp in the BYDV resistant materials containing the chromosome 2Ai-2, including Th. intermedium, wheat-Th. intermedium partial amphipoild Zhong 4 Awnless, addition lines Z1, Z2 and Z6, F1(Z2/Wan7107) and substitute line ZD28 etc, but absent in all the materials lacking the 2Ai-2 chromosome, including susceptible wheat parents and other wheat-Th. intermedium addition lines L1 and Z4. The RAPD markers specific to chromosome 2Ai-2, OPO05(650) and OPM04(1400), may be located on the St genomic region of 2Ai-2 chromosome by PCR analysis on Th. intermedium (E1E2St), Pseuderogneria strigosa (St), Th. elongatum (E), Haynaldia villosa (V), Secale cereale (R), Hordeum vulgare (H), Aegilops squrrosa (D) and Triticum aestivum (ABD) genomic DNA. The specific bands of RAPD markers OPO05(650) and OPM04(1400) were isolated and cloned. After the clones were subjected to restrict digestion analysis, PCR and Southern hybridization analysis, some clones were sequenced. Based on the sequences, 1 pair of primers SC-O5(U + L) and 1 pair of primers SC-M4(U + L) were designed, synthesized and used to amplify the materials with and without 2Ai-2 chromosome. The results showed that the SCAR markers of chromosome 2Ai-2, SC-O5 and SC-M4, were converted successfully from the RAPD markers OPO05(650) and OPM04(1400). The Th. intermedium fragments amplified by the primers of SC-O5 (U + L) and SCM4(U + L) were cloned and analyzed. The results of Southern hybridization indicated that TiSCO5, the cloned fragment of Th. intermedium amplified by primers of SC-O5(U + L) was a low-copy sequence specific to St genome, and another sequence TiSCM4, the cloned fragment of Th. intermedium amplified by primers of SC-M4(U + L) was a repeat sequence specific to St genomic. The sequences will be new probes to detect St genomic chromatin.