Biomedical subjects

Da Chen

Publications and source records attributed to Da Chen.

15 recordsLinked to original sources

PubMed2006

An adaptive strategy for selecting representative calibration samples in the continuous wavelet domain for near-infrared spectral analysis.

Sample selection is often used to improve the cost-effectiveness of near-infrared (NIR) spectral analysis. When raw NIR spectra are used, however, it is not easy to select appropriate samples, because of background interference and noise. In this paper, a novel adaptive strategy based on selection of representative NIR spectra in the continuous wavelet transform (CWT) domain is described. After pretreatment with the CWT, an extension of the Kennard-Stone (EKS) algorithm was used to adaptively select the most representative NIR spectra, which were then submitted to expensive chemical measurement and multivariate calibration. With the samples selected, a PLS model was finally built for prediction. It is of great interest to find that selection of representative samples in the CWT domain, rather than raw spectra, not only effectively eliminates background interference and noise but also further reduces the number of samples required for a good calibration, resulting in a high-quality regression model that is similar to the model obtained by use of all the samples. The results indicate that the proposed method can effectively enhance the cost-effectiveness of NIR spectral analysis. The strategy proposed here can also be applied to different analytical data for multivariate calibration.

Journal Article↗

PubMed2006

Photoacoustic and luminescence spectra study on the effects of chlorine substituent on the energy transfer of Eu(III)-chlorobenzoic acid.

The photoacoustic (PA) amplitude spectra of three complexes of Eu(III) combined with chlorobenzoic acid (Eu(o-ClC6H4CO2)3.H2O, Eu(m-ClC6H4CO2)3.H2O and Eu(p-ClC6H4CO2)3.H2O) have been measured, and the PA phase of the different complexes have been calculated. Both the PA amplitude spectra and the luminescence spectra reflect the variation of the luminescent properties, and the PA phase is directly relative to the relaxation time. Since the relaxation is the process of the intramolecular energy transfer between the ligands and the central ion, the molecular structure of ligand is the important factor to decide the energy gap between the lowest triplet state of ligand and the resonance level of central ion. The effects of chlorine substituent on the molecular structure and energy gap of the complexes have been studied by PA phase and luminescence spectra.

Acoustics↗

PubMed2005

Photoacoustic phase study on the frequency dependence of phase angle and triplet state lifetime of Nd(III)-acetylacetonate.

The amplitude and phase of the photoacoustic (PA) signal generated in the rare earth complex powder of Nd(III)-acetylacetonate (Nd(AA)3) were examined. By using the reasonably simplified formula about phase angle at the wavelengths assigned to pi-pi* transition of ligand and f-f transitions of Nd3+, the instrumental contribution to phase angle at different chopping frequency was calculated. The frequency dependence of sample phase angle, the relative phase angle shift caused by instrumental factors and the calculation of triplet state lifetime of sample under study were also discussed. Being independent of sample, the instrumental contribution to phase angle was regarded as a parameter representing the situations of instruments and measurement and it became an approach to calculate the relaxation time of ligand in rare earth complex.

Acoustics↗

PubMed2005

Simultaneous wavelength selection and outlier detection in multivariate regression of near-infrared spectra.

Near-infrared (NIR) spectrometry will present a more promising tool for quantitative measurement if the robustness and predictive ability of the partial least square (PLS) model are improved. In order to achieve the purpose, we present a new algorithm for simultaneous wavelength selection and outlier detection; at the same time, the problems of background and noise in multivariate calibration are also solved. The strategy is a combination of continuous wavelet transform (CWT) and modified iterative predictors and objects weighting PLS (mIPOW-PLS). CWT is performed as a pretreatment tool for eliminating background and noise synchronously; then, mIPOW-PLS is proposed to remove both the useless wavelengths and the multiple outliers in CWT domain. After pretreatment with CWT-mIPOW-PLS, a PLS model is built finally for prediction. The results indicate that the combination of CWT and mIPOW-PLS produces robust and parsimonious regression models with very few wavelengths.

Journal Article↗

PubMed2005

[The relationship between the expression of HIF-1alpha and the angiogenesis in infancy hemangioma].

OBJECTIVE: To investigate the expression of HIF-1alpha and its roles on the vascular endothelial cell growth factor (VEGF) and microvessel density (MVD ) in hemangioma. METHODS: Immunohistochemical streptavidin/peroxidase(SP) stain was applied to examine the expression of HIF-1alpha, VEGF and CD34. The amount of microvessel was counted, which the endothelial cell expressed CD34. RESULTS: The nuclei and cytoplasm of the endothelial cell showed positive staining for HIF-1alpha in hemangioma. In 28 cases, positive rate for HIF-1alpha was 64%, for VEGF was 71.4%. In the proliferating phase, positive rate for HIF-1alpha was 87.5%, for VEGF was 93.7%. However, the positive rate for HIF-1alpha, in the involuting phase, was 33.3%, and for VEGF was 41.7%. There was a very significantly different between two phases (P < 0.01). In the proliferating phase, MVD was 73.4 +/- 14.63 . In the involuting phase, MVD was 30.2 +/- 9.1 (P < 0.01). The correlation between the HIF-1alpha and VEGF was positive (P < 0.01). There was a positive correlation between the HIF-1alpha and MVD (P < 0.01). CONCLUSIONS: There might be a special hypoxia microenvironment in endothelial cell of the hemangioma in proliferating phase , which could up-regulate the expression of the HIF-1alpha protein. The HIF-1alpha protein could also up-regulate the VEGF protein and then result in the angiogenesis.

Adolescent↗

PubMed2005

[Analysis of multi-component sugar aqueous solution in low-concentration by near-infrared spectrometry].

Near infrared spectrophotometry was used to determine the concentrations of one, two and three-component sugar aqueous solutions. However, this method was always applied to dry or low moisture products and was not practicable for fresh fruits and vegetables because of the strong absorption of water in near infrared region. In this paper, the authors applied NIR method to aqueous solutions and discussed how to enhance the sensitivity. In aqueous solution systems, concentration of each individual sugar was in range of 0.01-0.25 mol x L(-1). Different calibrations and predicted results were gotten and compared to each other when full spectra or significant spectra regions were considered. By selecting relevant spectra regions due to important structural information to overcome the disturbance from absorption of water, calculations could be optimized and predicted results of concentrations were more accurate regarding the standard error of calibration (SEC) and standard error of prediction (SEP).

Calibration↗

PubMed2005

[A study on cytocompatibility of poly (lactic acid) membrane modified by polymer microspheres with different surface charges].

Poly(lactic acid) microspheres with different surface charges have been prepared by using cationic, anionic or nonionic surfactants as the microspheres' surface stabilizers. Embedded with these microspheres, the modified PLA membranes with different surface charges have been obtained. The test of stability by CLSM and the morphological test by SEM confirmed that we obtained the microspheres modified PLA membranes with different surface charges successfully. The chondrocyte compatibility test of these modified PLA membranes showed that the attachment, proliferation and activity of chondrocytes on the positive surface of the modified PLA were better than those of other modified PLA membranes. The positive charge on the surface of PLA membrane could improve the cell-compatibility of PLA well.

Animals↗

PubMed2004

A new hybrid strategy for constructing a robust calibration model for near-infrared spectral analysis.

A new hybrid algorithm is proposed for construction of a high-quality calibration model for near-infrared (NIR) spectra that is robust against both spectral interference (including background and noise) and multiple outliers. The algorithm is a combination of continuous wavelet transform (CWT) and a modified iterative reweighted PLS (mIRPLS) procedure. In the proposed algorithm the spectral interference is filtered by CWT at the first stage then mIRPLS is proposed to detect the multiple outliers in the CWT domain. Compared with the original IRPLS method, mIRPLS does not need to adjust variable parameters to achieve optimum calibration results, which makes it very convenient to perform in practice. The final PLS model is constructed robustly because both the spectral interference and multiple outliers are eliminated. In order to validate the effectiveness and universality of the algorithm, it was applied to two different sets of NIR spectra. The results indicate that the proposed strategy can greatly enhance the robustness and predictive ability of NIR spectral analysis.

Journal Article↗

PubMed2004

Variable selection by modified IPW (iterative predictor weighting)-PLS (partial least squares) in continuous wavelet regression models.

Variable selection is often used to produce more robust and parsimonious regression models. But when they are applied directly to the raw near-infrared spectra, it is not easy to select appropriate variables because background and noise will often overshadow or overlap the absorption bands of analyte. In this work, a new hybrid algorithm based on the selection of the most informative variables in the continuous wavelet transform (CWT) domain is described. The strategy is a combination of CWT and a procedure of modified iterative predictor weighting-partial least square (mIPW-PLS). After elimination of the background and noise in NIR spectra by CWT, the mIPW-PLS approach is used to select the most informative CWT coefficients. With the selected CWT coefficients, a PLS model is built finally for prediction. It is indicated that the extraction of most important variables in the CWT domain can effectively avoid the interference of background and noise, and result in a high quality of regression model with a very small number of variables and fewer PLS components.

Journal Article↗

PubMed2004

Removal of major interference sources in aqueous near-infrared spectroscopy techniques.

This work describes a hybrid procedure for eliminating major interference sources in aqueous near-infrared (NIR) spectra, that include aqueous influence, noise, and systemic variations irrelevant to concentration. The scheme consists of two parts: extension of wavelet prism (WPe) and orthogonal signal correction (OSC). First, WPe is employed to remove variations due to aqueous absorbance and noise; then OSC is applied to remove systemic spectral variations irrelevant to concentration. Although water possesses strong absorption bands that overshadow and overlap the absorption bands of analytes, along with noise and systematic interference, successful calibration models can be generated by employing the method proposed here. We show that the elimination of major interference sources from the aqueous NIR spectra results in a substantial improvement in the precision of prediction, and reduces the required number of PLS components in the model. In addition, the strategy proposed here can be applied to various analytical data for quantitative purposes as well.

Fructose↗

PubMed2004

A method for near-infrared spectral calibration of complex plant samples with wavelet transform and elimination of uninformative variables.

An algorithm is proposed for extracting relevant information from near-infrared (NIR) spectra for multivariate calibration of routine components in complex plant samples. The algorithm is a combination of wavelet transform (WT) data compression and a procedure for uninformative variable elimination (UVE). After compression of the NIR spectra by WT, the UVE approach is used to eliminate the irrelevant wavelet coefficients. Finally, a calibration model is built from the retained wavelet coefficients to enable prediction. Because irrelevant information can be removed from the spectra used for multivariate calibration, the model based on the extracted relevant features is better than those obtained with full-spectrum data. Both prediction precision and calculation speed are improved.

Journal Article↗

PubMed2004

Holographic QSAR of selected esters.

The HQSAR (Holographic QSAR) method, which has been recently developed, can offer the ability to rapidly and easily generate QSAR models of high statistical quality and predictive value. HQSAR analysis requires selecting values for parameters that specify the size of the hologram that is to be used, and the size and type of fragment substructures that are to be encoded. The color coding is provided by HQSAR to reflect which molecular fragments may be important contributors to the biological activity. In this work, we studied the quantitative structure activity relationship of selected esters using the HQSAR method. A robust HQSAR model with r(2) (non-cross-validated regression coefficient) of 0.981 and q(2) (cross-validated regression coefficient) of 0.912, was developed after optimizing the fragment size and the hologram length. The color coding analysis, which has rarely been reported before, was done here to explain the outlier successfully.

Animals↗

PubMed2004

[Preliminary experience of 16-layer three-dimensional computed tomography in diagnosis and treatment of arteriovenous malformations].

PURPOSE: We assessed the value of 16-layer three-dimensional computed tomography angiography (3D-CTA) and digital subtraction angiography (DSA) in diagnosis of the arteriovenous malformations (AVM). METHODS: 16 patients with AVM were examined by 16 layers CT scan and DSA. RESULTS: The DSA imaging provided excellent visualization in all of patients, including size, location, and feeding arterial of AVM. The value of the diagnosis of the nidus malformation vascular by 3D-CTA was similar to that by DSA, however, CTA was not good at diagnosis of the third feeding artery of AVM. The three-dimensional reconstruction also further revealed the relation of lesion and surrounding tissue which is helpful in making an appropriate decision before treatment. Differences in dates were compared using the t test. P<0.05 was considered statistically significant. CONCLUSION: 16-layer 3D-CTA was a superior approach for diagnosis and follow up of the AVM.

Adolescent↗

PubMed2004

[A novel method for the determination of inorganic ions in complex plant samples by near infrared spectroscopy].

Inorganic ions in plant samples can be determined by near-infrared (NIR) spectral technique, because they are combined with organic groups with NIR absorption. A method for the determination of inorganic ions in complex plant samples was established based on the combination of discrete wavelet transform (DWT) and NIR technique. In the proposed method, the raw NIR data and their wavelet coefficients are used for modeling and prediction of the contents of potassium in tobaccos by partial least square method (PLS). It is shown that there is almost no loss of spectral information with the NIR data compressed to 3.3% of its original size. The model based on wavelet coefficients is better than that based on the full NIR spectral range. With the improved method, accurate prediction can be achieved.

Ions↗

PubMed2003

[Staging and management of extracranial arteriovenous malformations].

OBJECTIVE: Congenital arteriovenous malformations(AVM) are considered to be the most difficult and challenging problems in the treatment of hemangiomas and vascular lesions. This study focused on the natural history, the clinical classification, the choice and effectiveness of various treatments. METHODS: This retrospective review included 83 patients with extracranial arteriovenous malformations, who were referred to our department over the past 6 years. The anatomic patterns, clinical staging, respective treatments, influential factors of endovascular treatment, causes of recurrence were analyzed. RESULTS: According to clinical manifestations, arteriovenous malformations were categorized as three clinical stages: the quiescence, the expansion and the decompensation stages. Most AVMS in the quiescence stage only require endovascular treatment while those in the decompensation stage require surgical resection. Angiography was performed not only for diagnosis of AVM but also as an initial therapeutic step in the form of embolization, which might be the only means to some AVM without surgical possibility or necessity. CONCLUSION: The new concept of staging and management is expected to be helpful for diagnosis and treatments of AVM.

Acrylates↗