Wei Lu - Academia.edu (original) (raw)

Papers by Wei Lu

Nanoscale Research Letters, 2008

We present a systemic theoretical study of the electronic properties of the quantum dots inserted... more We present a systemic theoretical study of the electronic properties of the quantum dots inserted in quantum dot infrared photodetectors (QDIPs). The strain distribution of three different shaped quantum dots (QDs) with a same ratio of the base to the vertical aspect is calculated by using the short-range valence-force-field (VFF) approach. The calculated results show that the hydrostatic strain e H varies little with change of the shape, while the biaxial strain e B changes a lot for different shapes of QDs. The recursion method is used to calculate the energy levels of the bound states in QDs. Compared with the strain, the shape plays a key role in the difference of electronic bound energy levels. The numerical results show that the deference of bound energy levels of lenslike InAs QD matches well with the experimental results. Moreover, the pyramidshaped QD has the greatest difference from the measured experimental data.

Nanomedicine, 2010

Copper sulfide (CuS) nanoparticles were developed as a new type of agent for photothermal ablatio... more Copper sulfide (CuS) nanoparticles were developed as a new type of agent for photothermal ablation of cancer cells. Materials & methods: CuS nanoparticles were synthesized by wet chemistry and their application in photothermal ablation of tumor cells was tested by irradiation using a near-infrared (NIR) laser beam at 808 nm to elevate the temperature of aqueous solutions of CuS nanoparticles as a function of exposure time and nanoparticle concentration. CuS nanoparticle-mediated photothermal destruction was evaluated using human cervical cancer HeLa cells with respect to laser dose and nanoparticle concentration. Their toxicity was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Results: CuS nanoparticles have an optical absorption band in the NIR range with a maximum absorbance at 900 nm. Irradiation by a NIR laser beam at 808 nm resulted in an increase in the temperature of the CuS nanoparticle aqueous solution as a function of exposure time and nanoparticle concentration. CuS nanoparticle-induced photothermal destruction of HeLa cells occured in a laser dose-and nanoparticle concentration-dependent manner, and displayed minimal cytotoxic effects with a profile similar to that of gold nanoparticles. Conclusion: Owing to their unique optical property, small size, low cost of production and low cytotoxicity, CuS nanoparticles are promising new nanomaterials for cancer photothermal ablation therapy.

Nano Research, 2014

We report a novel chemical vapor deposition (CVD) based strategy to synthesize carbon-coated Fe 2... more We report a novel chemical vapor deposition (CVD) based strategy to synthesize carbon-coated Fe 2 O 3 nanoparticles dispersed on graphene sheets (Fe 2 O 3 @C@G). Graphene sheets with high surface area and aspect ratio are chosen as space restrictor to prevent the sintering and aggregation of nanoparticles during high temperature treatments (800 °C ). In the resulting nanocomposite, each individual Fe 2 O 3 nanoparticle (5 to 20 nm in diameter) is uniformly coated with a continuous and thin (two to five layers) graphitic carbon shell. Further, the core-shell nanoparticles are evenly distributed on graphene sheets. When used as anode materials for lithium ion batteries, the conductive-additive-free Fe 2 O 3 @C@G electrode shows outstanding Li + storage properties with large reversible specific capacity (864 mAh/g after 100 cycles), excellent cyclic stability (120% retention after 100 cycles at 100 mA/g), high Coulombic efficiency (~99%), and good rate capability.

Nano Letters, 2005

We report low-temperature electrical transport studies of molecule-scale silicon nanowires. Indiv... more We report low-temperature electrical transport studies of molecule-scale silicon nanowires. Individual nanowires exhibit well-defined Coulomb blockade oscillations characteristic of charge addition to a single structure with length scales of at least 400 nm. Further studies demonstrate coherent charge transport through discrete single particle levels extending the whole devices, and show that the ground state spin follows the Lieb-Mattis theorem. In addition, depletion of the nanowires suggests that phase coherent single-dot characteristics are accessible in a regime where correlations are strong. PACS numbers: 73.63.Nm, 73.23.Hk, Studies of carbon nanotubes [1] and semiconductor nanowires [2] have demonstrated their potential as building blocks for nanoscale electronics. An advantage of these building blocks versus nanostructures fabricated by 'top-down' processing is that, critical nanoscale features are defined during synthesis, which can yield uniform structures at the atomic scale. Indeed, isolated carbon nanotube transistors have shown exceptional properties [3], although difficulties in preparing pure semiconductor nanotubes make large scale integration challenging. Silicon nanowires (SiNWs) could overcome issues faced by nanotubes since current growth methods enable reproducible control over both size and electronic properties of the nanowires . Recent studies have begun to elucidate fundamental transport properties of chemically-synthesized semiconducting nanowires , which are required to move beyond initial roomtemperature devices assembled with SiNWs [5, 8]; however, similar fundamental studies of SiNWs have not been reported. In this Letter we address this critical issue through low-temperature electrical transport measurements on molecular-scale SiNWs configured as singleelectron transistors (SETs).

Nano Letters, 2010

We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell na... more We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell nanowires. Negative magneto-conductance was observed, which is a signature of one-dimensional weak antilocalization of holes in the presence of strong spin-orbit coupling. The temperature and back gate dependences of phase coherence length, spin-orbit relaxation time, and background conductance were studied. Specifically, we show the spin-orbit coupling strength can be modulated by more than five folds with an external electric field. These results suggest the Ge/Si nanowire system possesses strong and tunable spin-orbit interactions and may serve as a candidate for spintronics applications.

Nano Letters, 2008

Radial core/shell nanowires (NWs) represent an important class of nanoscale building blocks with ... more Radial core/shell nanowires (NWs) represent an important class of nanoscale building blocks with substantial potential for exploring fundamental electronic properties and realizing novel device applications at the nanoscale. Here, we report the synthesis of crystalline silicon/amorphous silicon (Si/a-Si) core/shell NWs and studies of crossed Si/a-Si NW metal NW (Si/a-Si × M) devices and arrays. Room-temperature electrical measurements on single Si/a-Si × Ag NW devices exhibit bistable switching between high (off) and low (on) resistance states with well-defined switching threshold voltages, on/off ratios greater than 10 4 , and current rectification in the on state.

Molecular Imaging and Biology, 2011

Purpose: We examined the biodistribution and pharmacokinetics of 111 In-labeled rGel/BLyS, a gelo... more Purpose: We examined the biodistribution and pharmacokinetics of 111 In-labeled rGel/BLyS, a gelonin toxin (rGel)-B lymphocyte stimulator (BLyS) fusion protein.

Molecular Genetics and Metabolism, 2006

Folate binding protein 1 (Folr1) knockout mice with low maternal folate concentrations have been ... more Folate binding protein 1 (Folr1) knockout mice with low maternal folate concentrations have been shown to be excellent animal models for human folate-responsive neural tube defects (NTDs). Previous studies using the Folr1 knockout mice revealed that maternal folate supplementation upregulates the expression of the PCMT1 gene in Folr1 nullizygous neural tube tissue during neural tube closure. PCMT1 encodes the protein repair enzyme L-isoaspartate (D-aspartate) Omethyltransferase (PIMT) that converts abnormal D-aspartyl and L-isoaspartyl residues to the normal L-aspartyl form. PIMT is known to protect certain neural cells from Bax-induced apoptosis. Pcmt1deficient mice present with abnormal AdoMet/AdoHcy homeostasis. We hypothesized that a known functional polymorphism (Ile120Val) in the human PCMT1 gene is associated with an increased risk of folate-responsive human NTDs. A case-control study was conducted to investigate a possible association between this polymorphism and risk of spina bifida. Compared to the Ile/Ile and Ile/Val genotypes, the homozygous Val/Val genotype showed decreased risk for spina bifida (adjusted odds ratio = 0.6, 95% confidence interval: 0.4-0.9). Our results showed that the Ile120Val polymorphism of PCMT1 gene is a genetic modifier for the risk of spina bifida. Val/Val genotype was associated with a reduction in risk for spina bifida.

Molecular BioSystems, 2011

Gram-negative bacterium Escherichia coli and the Gram-positive Deinococcus radiodurans fundamenta... more Gram-negative bacterium Escherichia coli and the Gram-positive Deinococcus radiodurans fundamentally differ in their cell structures and gene regulations. We have previously reported that IrrE, a Deinococcus genus-specific global regulator, confers significantly enhanced tolerance to various abiotic stresses. To better understand the global effects of IrrE on the regulatory networks, we carried out combined transcriptome and proteome analysis of E. coli expressing the IrrE protein. Our analysis showed that 216 (4.8%) of all E. coli genes were induced and 149 (3.3%) genes were repressed, including those for trehalose biosynthesis, nucleotides biosynthesis, carbon source utilization, amino acid utilization, acid resistance, a hydrogenase and an oxidase. Also regulated were the EvgSA two-component system, the GadE, GadX and PurR master regulators, and 10 transcription factors (AppY, GadW, YhiF, AsnC, BetI, CynR, MhpR, PrpR, TdcA and KdgR). These results demonstrated that IrrE acts as global regulator and consequently improves abiotic stress tolerances in the heterologous host E. coli. The implication of our findings is discussed in relation to the evolutionary role of horizontal gene transfer in bacterial regulatory networks and environmental adaptation.

Molecular and Cellular Biochemistry, 2005

In the postgenomic era the elucidation of the physiological function of genes has become the rate... more In the postgenomic era the elucidation of the physiological function of genes has become the rate-limiting step in the quest to understand the development and function of living organisms. Double-stranded RNA (dsRNA) interferes with gene expression in various species, a phenomenon known as RNA interference (RNAi). We show here that RNAi is also effective in modifying gene expression in neural stem cell differentiation. The progenitor cells were obtained from E14 mouse embryonic forebrain and maintained using N-2 medium containing basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and B27.A gene (NM017084.1) was previously discovered and validated to express obviously differently between differentiated and undifferentiated neural stem cells in our laboratory. Here we report a long double-stranded RNA to knock out or knock down this gene. The results demonstrated that following RNAi inhibition of expression of the NM017084.1 gene, the differentiation of neural stem cells is accelerated. Thus the NM017084.1 gene may play a pivotal role in the process of differentiation of neural stem cells. (Mol Cell Biochem 275: 215-221, 2005)

Microelectronic Engineering, 2010

ABSTRACT In this paper, we present the nanofabrication of a potentially coupled waveguide–surface... more ABSTRACT In this paper, we present the nanofabrication of a potentially coupled waveguide–surface plasmon resonance biosensor (CWSPRBs) by nanoimprint lithography. Subwavelength metallic gratings (SWMGs) with the pitches of 300 and 500nm were fabricated by direct imprinting on PMMA layer which subsequently covered with a layer of Au. The key issue in this device is the coupling of surface plasmon with waveguide modes, which has been carefully investigated by measuring the coupling induced enhancement of light transmission. Both our measurement and simulation results indicate that the resonant coupling does exist for both 300 and 500nm pitched gratings. This proves that the developed nanoimprint lithography is applicable for the CWSPRBs sensors which has significant advantages over traditional ones with a prism.

Medical Physics, 2008

Four-dimensional computed tomography ͑4D-CT͒ imaging technology has been developed for radiation ... more Four-dimensional computed tomography ͑4D-CT͒ imaging technology has been developed for radiation therapy to provide tumor and organ images at the different breathing phases. In this work, a procedure is proposed for estimating and modeling the respiratory motion field from acquired 4D-CT imaging data and predicting tissue motion at the different breathing phases. The 4D-CT image data consist of series of multislice CT volume segments acquired in ciné mode. A modified optical flow deformable image registration algorithm is used to compute the image motion from the CT segments to a common full volume 3D-CT reference. This reference volume is reconstructed using the acquired 4D-CT data at the end-of-exhalation phase. The segments are optimally aligned to the reference volume according to a proposed a priori alignment procedure. The registration is applied using a multigrid approach and a feature-preserving image downsampling maxfilter to achieve better computational speed and higher registration accuracy. The registration accuracy is about 1.1Ϯ 0.8 mm for the lung region according to our verification using manually selected landmarks and artificially deformed CT volumes. The estimated motion fields are fitted to two 5D ͑spatial 3D + tidal volume+ airflow rate͒ motion models: forward model and inverse model. The forward model predicts tissue movements and the inverse model predicts CT density changes as a function of tidal volume and airflow rate. A leave-one-out procedure is used to validate these motion models. The estimated modeling prediction errors are about 0.3 mm for the forward model and 0.4 mm for the inverse model.

Medical Physics, 2010

Purpose: To quantitatively test a breathing motion model using the continuity equation and clinic... more Purpose: To quantitatively test a breathing motion model using the continuity equation and clinical data. Methods: The continuity equation was applied to a lung tissue and lung tumor free breathing motion model to quantitatively test the model performance. The model used tidal volume and airflow as the independent variables and the ratio of motion to tidal volume and motion to airflow were defined as ␣ ជ and ␤ ជ vector fields, respectively. The continuity equation resulted in a prediction that the volume integral of the divergence of the ␣ ជ vector field was 1.11 for all patients. The integral of the divergence of the ␤ ជ vector field was expected to be zero. Results: For 35 patients, the ␣ ជ vector field prediction was 1.06Ϯ 0.14, encompassing the expected value. For the ␤ ជ vector field prediction, the average value was 0.02Ϯ 0.03. Conclusions: These results provide quantitative evidence that the breathing motion model yields accurate predictions of breathing dynamics.

Medical Physics, 2010

In radiation therapy applications, deformable image registrations (DIRs) are often carried out be... more In radiation therapy applications, deformable image registrations (DIRs) are often carried out between two images that only partially match. Image mismatching could present as superior-inferior coverage differences, field-of-view (FOV) cutoffs, or motion crossing the image boundaries. In this study, the authors propose a method to improve the existing DIR algorithms so that DIR can be carried out in such situations. The basic idea is to extend the image volumes and define the extension voxels (outside the FOV or outside the original image volume) as NaN (not-a-number) values that are transparent to all floating-point computations in the DIR algorithms. Registrations are then carried out with one additional rule that NaN voxels can match any voxels. In this way, the matched sections of the images are registered properly, and the mismatched sections of the images are registered to NaN voxels. This method makes it possible to perform DIR on partially matched images that otherwise are difficult to register. It may also improve DIR accuracy, especially near or in the mismatched image regions.

Nanoscale Research Letters, 2008

We present a systemic theoretical study of the electronic properties of the quantum dots inserted... more We present a systemic theoretical study of the electronic properties of the quantum dots inserted in quantum dot infrared photodetectors (QDIPs). The strain distribution of three different shaped quantum dots (QDs) with a same ratio of the base to the vertical aspect is calculated by using the short-range valence-force-field (VFF) approach. The calculated results show that the hydrostatic strain e H varies little with change of the shape, while the biaxial strain e B changes a lot for different shapes of QDs. The recursion method is used to calculate the energy levels of the bound states in QDs. Compared with the strain, the shape plays a key role in the difference of electronic bound energy levels. The numerical results show that the deference of bound energy levels of lenslike InAs QD matches well with the experimental results. Moreover, the pyramidshaped QD has the greatest difference from the measured experimental data.

Nanomedicine, 2010

Copper sulfide (CuS) nanoparticles were developed as a new type of agent for photothermal ablatio... more Copper sulfide (CuS) nanoparticles were developed as a new type of agent for photothermal ablation of cancer cells. Materials & methods: CuS nanoparticles were synthesized by wet chemistry and their application in photothermal ablation of tumor cells was tested by irradiation using a near-infrared (NIR) laser beam at 808 nm to elevate the temperature of aqueous solutions of CuS nanoparticles as a function of exposure time and nanoparticle concentration. CuS nanoparticle-mediated photothermal destruction was evaluated using human cervical cancer HeLa cells with respect to laser dose and nanoparticle concentration. Their toxicity was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Results: CuS nanoparticles have an optical absorption band in the NIR range with a maximum absorbance at 900 nm. Irradiation by a NIR laser beam at 808 nm resulted in an increase in the temperature of the CuS nanoparticle aqueous solution as a function of exposure time and nanoparticle concentration. CuS nanoparticle-induced photothermal destruction of HeLa cells occured in a laser dose-and nanoparticle concentration-dependent manner, and displayed minimal cytotoxic effects with a profile similar to that of gold nanoparticles. Conclusion: Owing to their unique optical property, small size, low cost of production and low cytotoxicity, CuS nanoparticles are promising new nanomaterials for cancer photothermal ablation therapy.

Nano Research, 2014

We report a novel chemical vapor deposition (CVD) based strategy to synthesize carbon-coated Fe 2... more We report a novel chemical vapor deposition (CVD) based strategy to synthesize carbon-coated Fe 2 O 3 nanoparticles dispersed on graphene sheets (Fe 2 O 3 @C@G). Graphene sheets with high surface area and aspect ratio are chosen as space restrictor to prevent the sintering and aggregation of nanoparticles during high temperature treatments (800 °C ). In the resulting nanocomposite, each individual Fe 2 O 3 nanoparticle (5 to 20 nm in diameter) is uniformly coated with a continuous and thin (two to five layers) graphitic carbon shell. Further, the core-shell nanoparticles are evenly distributed on graphene sheets. When used as anode materials for lithium ion batteries, the conductive-additive-free Fe 2 O 3 @C@G electrode shows outstanding Li + storage properties with large reversible specific capacity (864 mAh/g after 100 cycles), excellent cyclic stability (120% retention after 100 cycles at 100 mA/g), high Coulombic efficiency (~99%), and good rate capability.

Nano Letters, 2005

We report low-temperature electrical transport studies of molecule-scale silicon nanowires. Indiv... more We report low-temperature electrical transport studies of molecule-scale silicon nanowires. Individual nanowires exhibit well-defined Coulomb blockade oscillations characteristic of charge addition to a single structure with length scales of at least 400 nm. Further studies demonstrate coherent charge transport through discrete single particle levels extending the whole devices, and show that the ground state spin follows the Lieb-Mattis theorem. In addition, depletion of the nanowires suggests that phase coherent single-dot characteristics are accessible in a regime where correlations are strong. PACS numbers: 73.63.Nm, 73.23.Hk, Studies of carbon nanotubes [1] and semiconductor nanowires [2] have demonstrated their potential as building blocks for nanoscale electronics. An advantage of these building blocks versus nanostructures fabricated by 'top-down' processing is that, critical nanoscale features are defined during synthesis, which can yield uniform structures at the atomic scale. Indeed, isolated carbon nanotube transistors have shown exceptional properties [3], although difficulties in preparing pure semiconductor nanotubes make large scale integration challenging. Silicon nanowires (SiNWs) could overcome issues faced by nanotubes since current growth methods enable reproducible control over both size and electronic properties of the nanowires . Recent studies have begun to elucidate fundamental transport properties of chemically-synthesized semiconducting nanowires , which are required to move beyond initial roomtemperature devices assembled with SiNWs [5, 8]; however, similar fundamental studies of SiNWs have not been reported. In this Letter we address this critical issue through low-temperature electrical transport measurements on molecular-scale SiNWs configured as singleelectron transistors (SETs).

Nano Letters, 2010

We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell na... more We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell nanowires. Negative magneto-conductance was observed, which is a signature of one-dimensional weak antilocalization of holes in the presence of strong spin-orbit coupling. The temperature and back gate dependences of phase coherence length, spin-orbit relaxation time, and background conductance were studied. Specifically, we show the spin-orbit coupling strength can be modulated by more than five folds with an external electric field. These results suggest the Ge/Si nanowire system possesses strong and tunable spin-orbit interactions and may serve as a candidate for spintronics applications.

Nano Letters, 2008

Radial core/shell nanowires (NWs) represent an important class of nanoscale building blocks with ... more Radial core/shell nanowires (NWs) represent an important class of nanoscale building blocks with substantial potential for exploring fundamental electronic properties and realizing novel device applications at the nanoscale. Here, we report the synthesis of crystalline silicon/amorphous silicon (Si/a-Si) core/shell NWs and studies of crossed Si/a-Si NW metal NW (Si/a-Si × M) devices and arrays. Room-temperature electrical measurements on single Si/a-Si × Ag NW devices exhibit bistable switching between high (off) and low (on) resistance states with well-defined switching threshold voltages, on/off ratios greater than 10 4 , and current rectification in the on state.

Molecular Imaging and Biology, 2011

Purpose: We examined the biodistribution and pharmacokinetics of 111 In-labeled rGel/BLyS, a gelo... more Purpose: We examined the biodistribution and pharmacokinetics of 111 In-labeled rGel/BLyS, a gelonin toxin (rGel)-B lymphocyte stimulator (BLyS) fusion protein.

Molecular Genetics and Metabolism, 2006

Folate binding protein 1 (Folr1) knockout mice with low maternal folate concentrations have been ... more Folate binding protein 1 (Folr1) knockout mice with low maternal folate concentrations have been shown to be excellent animal models for human folate-responsive neural tube defects (NTDs). Previous studies using the Folr1 knockout mice revealed that maternal folate supplementation upregulates the expression of the PCMT1 gene in Folr1 nullizygous neural tube tissue during neural tube closure. PCMT1 encodes the protein repair enzyme L-isoaspartate (D-aspartate) Omethyltransferase (PIMT) that converts abnormal D-aspartyl and L-isoaspartyl residues to the normal L-aspartyl form. PIMT is known to protect certain neural cells from Bax-induced apoptosis. Pcmt1deficient mice present with abnormal AdoMet/AdoHcy homeostasis. We hypothesized that a known functional polymorphism (Ile120Val) in the human PCMT1 gene is associated with an increased risk of folate-responsive human NTDs. A case-control study was conducted to investigate a possible association between this polymorphism and risk of spina bifida. Compared to the Ile/Ile and Ile/Val genotypes, the homozygous Val/Val genotype showed decreased risk for spina bifida (adjusted odds ratio = 0.6, 95% confidence interval: 0.4-0.9). Our results showed that the Ile120Val polymorphism of PCMT1 gene is a genetic modifier for the risk of spina bifida. Val/Val genotype was associated with a reduction in risk for spina bifida.

Molecular BioSystems, 2011

Gram-negative bacterium Escherichia coli and the Gram-positive Deinococcus radiodurans fundamenta... more Gram-negative bacterium Escherichia coli and the Gram-positive Deinococcus radiodurans fundamentally differ in their cell structures and gene regulations. We have previously reported that IrrE, a Deinococcus genus-specific global regulator, confers significantly enhanced tolerance to various abiotic stresses. To better understand the global effects of IrrE on the regulatory networks, we carried out combined transcriptome and proteome analysis of E. coli expressing the IrrE protein. Our analysis showed that 216 (4.8%) of all E. coli genes were induced and 149 (3.3%) genes were repressed, including those for trehalose biosynthesis, nucleotides biosynthesis, carbon source utilization, amino acid utilization, acid resistance, a hydrogenase and an oxidase. Also regulated were the EvgSA two-component system, the GadE, GadX and PurR master regulators, and 10 transcription factors (AppY, GadW, YhiF, AsnC, BetI, CynR, MhpR, PrpR, TdcA and KdgR). These results demonstrated that IrrE acts as global regulator and consequently improves abiotic stress tolerances in the heterologous host E. coli. The implication of our findings is discussed in relation to the evolutionary role of horizontal gene transfer in bacterial regulatory networks and environmental adaptation.

Molecular and Cellular Biochemistry, 2005

In the postgenomic era the elucidation of the physiological function of genes has become the rate... more In the postgenomic era the elucidation of the physiological function of genes has become the rate-limiting step in the quest to understand the development and function of living organisms. Double-stranded RNA (dsRNA) interferes with gene expression in various species, a phenomenon known as RNA interference (RNAi). We show here that RNAi is also effective in modifying gene expression in neural stem cell differentiation. The progenitor cells were obtained from E14 mouse embryonic forebrain and maintained using N-2 medium containing basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and B27.A gene (NM017084.1) was previously discovered and validated to express obviously differently between differentiated and undifferentiated neural stem cells in our laboratory. Here we report a long double-stranded RNA to knock out or knock down this gene. The results demonstrated that following RNAi inhibition of expression of the NM017084.1 gene, the differentiation of neural stem cells is accelerated. Thus the NM017084.1 gene may play a pivotal role in the process of differentiation of neural stem cells. (Mol Cell Biochem 275: 215-221, 2005)

Microelectronic Engineering, 2010

ABSTRACT In this paper, we present the nanofabrication of a potentially coupled waveguide–surface... more ABSTRACT In this paper, we present the nanofabrication of a potentially coupled waveguide–surface plasmon resonance biosensor (CWSPRBs) by nanoimprint lithography. Subwavelength metallic gratings (SWMGs) with the pitches of 300 and 500nm were fabricated by direct imprinting on PMMA layer which subsequently covered with a layer of Au. The key issue in this device is the coupling of surface plasmon with waveguide modes, which has been carefully investigated by measuring the coupling induced enhancement of light transmission. Both our measurement and simulation results indicate that the resonant coupling does exist for both 300 and 500nm pitched gratings. This proves that the developed nanoimprint lithography is applicable for the CWSPRBs sensors which has significant advantages over traditional ones with a prism.

Medical Physics, 2008

Four-dimensional computed tomography ͑4D-CT͒ imaging technology has been developed for radiation ... more Four-dimensional computed tomography ͑4D-CT͒ imaging technology has been developed for radiation therapy to provide tumor and organ images at the different breathing phases. In this work, a procedure is proposed for estimating and modeling the respiratory motion field from acquired 4D-CT imaging data and predicting tissue motion at the different breathing phases. The 4D-CT image data consist of series of multislice CT volume segments acquired in ciné mode. A modified optical flow deformable image registration algorithm is used to compute the image motion from the CT segments to a common full volume 3D-CT reference. This reference volume is reconstructed using the acquired 4D-CT data at the end-of-exhalation phase. The segments are optimally aligned to the reference volume according to a proposed a priori alignment procedure. The registration is applied using a multigrid approach and a feature-preserving image downsampling maxfilter to achieve better computational speed and higher registration accuracy. The registration accuracy is about 1.1Ϯ 0.8 mm for the lung region according to our verification using manually selected landmarks and artificially deformed CT volumes. The estimated motion fields are fitted to two 5D ͑spatial 3D + tidal volume+ airflow rate͒ motion models: forward model and inverse model. The forward model predicts tissue movements and the inverse model predicts CT density changes as a function of tidal volume and airflow rate. A leave-one-out procedure is used to validate these motion models. The estimated modeling prediction errors are about 0.3 mm for the forward model and 0.4 mm for the inverse model.

Medical Physics, 2010

Purpose: To quantitatively test a breathing motion model using the continuity equation and clinic... more Purpose: To quantitatively test a breathing motion model using the continuity equation and clinical data. Methods: The continuity equation was applied to a lung tissue and lung tumor free breathing motion model to quantitatively test the model performance. The model used tidal volume and airflow as the independent variables and the ratio of motion to tidal volume and motion to airflow were defined as ␣ ជ and ␤ ជ vector fields, respectively. The continuity equation resulted in a prediction that the volume integral of the divergence of the ␣ ជ vector field was 1.11 for all patients. The integral of the divergence of the ␤ ជ vector field was expected to be zero. Results: For 35 patients, the ␣ ជ vector field prediction was 1.06Ϯ 0.14, encompassing the expected value. For the ␤ ជ vector field prediction, the average value was 0.02Ϯ 0.03. Conclusions: These results provide quantitative evidence that the breathing motion model yields accurate predictions of breathing dynamics.

Medical Physics, 2010

In radiation therapy applications, deformable image registrations (DIRs) are often carried out be... more In radiation therapy applications, deformable image registrations (DIRs) are often carried out between two images that only partially match. Image mismatching could present as superior-inferior coverage differences, field-of-view (FOV) cutoffs, or motion crossing the image boundaries. In this study, the authors propose a method to improve the existing DIR algorithms so that DIR can be carried out in such situations. The basic idea is to extend the image volumes and define the extension voxels (outside the FOV or outside the original image volume) as NaN (not-a-number) values that are transparent to all floating-point computations in the DIR algorithms. Registrations are then carried out with one additional rule that NaN voxels can match any voxels. In this way, the matched sections of the images are registered properly, and the mismatched sections of the images are registered to NaN voxels. This method makes it possible to perform DIR on partially matched images that otherwise are difficult to register. It may also improve DIR accuracy, especially near or in the mismatched image regions.