Biomedical subjects

K W Yu

Publications and source records attributed to K W Yu.

At least 19 recordsLinked to original sources

PubMed2006

Dielectrophoresis of an inhomogeneous colloidal particle under an inhomogeneous field: a first-principles approach.

In reality, colloidal particles often possess an arbitrary inhomogeneity profile. We present a first-principles approach to dielectrophoresis of such an inhomogeneous colloidal particle under an inhomogeneous field of an oscillating electric dipole moment. For numerical simulations, we treat the inhomogeneous particle as a specific graded one with a physically motivated dielectric model and conductivity profile. We find that both multipolar interactions and spatial fluctuations inside the particle can affect the dielectrophoretic spectrum of the particle significantly.

Colloids↗

PubMed2006

Dynamic effects on nonlinear alternating current responses in electrorheological fluids.

By using a perturbation approach, we investigate dynamic effects on nonlinear alternating current (ac) responses in electrorheological (ER) fluids under an ac or direct current electric field. We show that the dynamic effect due to a shear flow, which exerts a torque on ER particles and thus leads to the rotation of the particles about their centers, plays a significant role in the responses. Our results can be well interpreted in the dielectric dispersion spectral representation, and they offer a convenient method to determine the relaxation time and rotation velocity of ER particles by measuring the nonlinear ac responses.

Journal Article↗

PubMed2005

Application of bioreactor system for large-scale production of Eleutherococcus sessiliflorus somatic embryos in an air-lift bioreactor and production of eleutherosides.

Embryogenic callus was induced from leaf explants of Eleutherococcus sessiliflorus cultured on Murashige and Skoog (MS) basal medium supplemented with 1 mg l(-1) 2,4-dichlorophenoxyacetic acid (2,4-D), while no plant growth regulators were needed for embryo maturation. The addition of 1 mg l(-1) 2,4-D was needed to maintain the embryogenic culture by preventing embryo maturation. Optimal embryo germination and plantlet development was achieved on MS medium with 4 mg l(-1) gibberellic acid (GA(3)). Low-strength MS medium (1/2 and 1/3 strength) was more effective than full-strength MS for the production of normal plantlets with well-developed shoots and roots. The plants were successfully transferred to soil. Embryogenic callus was used to establish a suspension culture for subsequent production of somatic embryos in bioreactor. By inoculating 10 g of embryogenic cells (fresh weight) into a 3l balloon type bubble bioreactor (BTBB) containing 2l MS medium without plant growth regulators, 121.8 g mature somatic embryos at different developmental stages were harvested and could be separated by filtration. Cotyledonary somatic embryos were germinated, and these converted into plantlets following transfer to a 3l BTBB containing 2l MS medium with 4 mg l(-1) GA3. HPLC analysis revealed that the total eleutherosides were significantly higher in leaves of field grown plants as compared to different stages of somatic embryo. However, the content of eleutheroside B was highest in germinated embryos. Germinated embryos also had higher contents of eleutheroside E and eleutheroside E1 as compared to other developmental stages. This result indicates that an efficient protocol for the mass production of E. sessiliflorus biomass can be achieved by bioreactor culture of somatic embryos and can be used as a source of medicinal raw materials.

Bioreactors↗

PubMed2005

Spectral representation of the effective dielectric constant of graded composites.

We generalize the Bergman-Milton spectral representation, originally derived for a two-component composite, to extract the spectral density function for the effective dielectric constant of a graded composite. This work has been motivated by a recent study of the optical absorption spectrum of a graded metallic film [Huang and Yu, Appl. Phys. Lett. 85, 94 (2004)] in which a broad surface-plasmon absorption band was shown to be responsible for enhanced nonlinear optical response and an attractive figure of merit. It turns out that, unlike in the case of homogeneous constituent components, the characteristic function of a graded composite is a continuous function because of the continuous variation of the dielectric function within the constituent components. Analytical generalization to three-dimensional graded composites is discussed, and numerical calculations for multilayer composites are given as a simple application.

Journal Article↗

PubMed2005

Computed tomography for cervical spine trauma. The impact of MDCT on fracture detection and dose deposition.

A multidetector computed tomography (MDCT) was installed in our department. Referral rates, examination protocols and detection rates of abnormal findings in CT examinations for cervical spine trauma 6 months before and 6 months after MDCT installation were compared to look for changes in practice. Retrospective analysis of all CT cervical spine examinations in patients with multiple trauma over two contiguous 6-month periods: from July 2003 to December 2003 (helical CT) and from January 2004 to June 2004 (MDCT). Variables recorded were number of CT examinations performed, scan plane coverage and traumatic abnormalities detected. Phantom dosimetry measurements for cervical spine examination in both helical CT and MDCT were compared. One hundred and fifty four patients underwent cervical spine CT during these periods. Helical CT period: of 91 patients undergoing CT cervical spine examination for trauma, 65 (71%) were complete cervical examinations and 26 (29%) were level-specific examinations. Eight patients (9%) had cervical spine fracture, six of which were apparent on radiographs. Dose estimations for thyroid, lens and breast were 24.76, 1.86 and 0.21 mGy, respectively, for complete cervical spine examinations. MDCT period: of 63 patients who underwent CT cervical spine examination for trauma, 61 (97%) were complete examinations and 2 (3%) were level-specific examinations. Six patients (11%) had cervical spine fracture, three of which were apparent on radiographs. Dose estimations for thyroid, lens and breast were 75.8, 9.7 and 0.7 mGy, respectively, for complete cervical spine examinations, which were notably higher than those for helical CT. After installation of MDCT, clinical requests for complete examination of the cervical spine following trauma increased. This changing trend resulted in a significantly higher radiation dose to thyroid, lens and breast.

Accidental Falls↗

PubMed2005

Second-harmonic generation in graded metallic films.

We study the effective second-harmonic generation (SHG) susceptibility in graded metallic films by invoking the local field effects exactly and further numerically demonstrate that graded metallic films can serve as a novel optical material for producing a broad structure in both the linear and the SHG response and an enhancement in the SHG signal.

Journal Article↗

PubMed2005

Theory of nondegenerate nonlinear optical susceptibilities of graded composites with high-volume fractions.

We present a theory for the effective nondegenerate third-order nonlinear optical susceptibility (NDTNOS) of composite media in which the graded metallic particles with weak nonlinearity and the linear dielectric grains are randomly distributed. In combination with an effective medium approximation, the recently established nonlinear differential effective dipole approximation (NDEDA), which is valid for the degenerate third-order optical nonlinearity of the composites in the dilute limit, is generalized to deal with the effective NDTNOS of graded composites of high-volume fractions. Numerical results show that for high-volume fractions, the presence of gradation makes the effective NDTNOS enhanced, but the linear optical absorption reduced, thus, yielding an attractive figure of merit. In addition, by using NDEDA and Maxwell-Garnett approximation, we study the effective NDTNOS of the graded composite media with the Hashin-Shtrikman microgeometry. The nondegenerate optical nonlinearity enhancement is found to be sensitive to the composite topology.

Journal Article↗

PubMed2005

Production of eleutherosides in in vitro regenerated embryos and plantlets of Eleutherococcus chiisanensis.

High frequency somatic embryogenesis of Eleutheorcoccus chiisanensis was achieved through suspension culture of embryogenic cells in hormone-free Murashige and Skoog liquid medium supplemented with 30 g sucrose l-1. Cotyledonary somatic embryos were germinated and converted into plantlets using 20 microM: gibberellic acid which were then grown in a 10 l airlift bioreactor. HPLC analysis revealed the accumulation of eleutheroside B, E and E1 in the embryos and plantlets. Thus mass production of embryos and plantlets of E. chiisanensis can be achieved in liquid cultures and the biomass produced may become an alternative source of eleutherosides.

Bioreactors↗

PubMed2005

Macrophage-stimulating activity of exo-biopolymer from cultured rice bran with Monascus pilosus.

To find a new use of rice bran, five fungi were examined for the production of exo-biopolymer with macrophage-stimulating activity from rice bran. Among the exo-biopolymers produced from the cultures, Monascus pilosus had the most potent macrophage stimulating activity in a liquid culture rather than in a solid culture. In order to improve the yield of exo-biopolymer with macrophage-stimulating activity, a suitable medium for exo-biopolymer was tested in submerged culture of M. pilosus. The highest amount of exo-biopolymer (13.9 mg/mL) was obtained in a medium containing rice bran as an only carbon source followed by media with additional maltose and sucrose (13.8 and 13.7 mg/mL, respectively). The addition of peptone resulted in the production of high amount of exo-biopolymer (15.1 mg/mL), meanwhile the addition of ammonium chloride resulted in 264.0 microg/mL of glucosamine content. Among eight different kinds of inorganic salts tested, potassium phosphate (0.1%) was the most effective inorganic salt for the mycelial growth and exo-biopolymer production. Therefore the optimal medium composition was as follows (g/L): 20 g of rice bran, 5 g of peptone, and 1 g of KH2PO4. The optimal culture pH and time for mycelial growth and exo-biopolymer production was pH 5.0 and 25 degrees C, respectively. The maximum exo-biopolymer (20.1 mg/mL) was observed at the fourth day of cultivation. Exo-biopolymer, a crude polysaccharide fraction, mainly contained neutral sugar (81.8%) with considerable amounts of uronic acid (18.2%). Component sugar analysis showed that the active fraction consisted mainly of arabinose, galactose, glucose, which was digested from starch of rice bran during cultivation, and uronic acid (molar ratio; 0.8:1.0:0.7:0.8).

Animals↗

PubMed2004

Interparticle force in electrorheological solids: many-body dipole-induced dipole model.

One often investigates electrorheological (ER) solids by using the point-dipole (PD) approximation, which, however, is known to err considerably for touching particles due to the existence of many-body (local-field) effects and multipolar interactions. Beyond the PD model, previous attempts have been restricted to either local-field effects only or multipolar interactions only, but not both. In the present work, we have developed a many-body dipole-induced dipole model for an ER solid the lattice structure of which can be changed due to the application of external fields, in an attempt to take into account both local-field effects and multipolar interactions. The results show that the multipolar interaction can indeed be dominant over the dipolar interaction, while the local-field effect may yield an important correction. Also, the results are well understood with the aid of spectral representation theory.

Journal Article↗

PubMed2004

Methyl jasmonate elicitation enhanced synthesis of ginsenoside by cell suspension cultures of Panax ginseng in 5-l balloon type bubble bioreactors.

The effects of methyl jasmonate (MJ) elicitation on the cell growth and accumulation of ginsenoside in 5-l bioreactor suspension cultures of Panax ginseng were investigated. Ginsenoside accumulation was enhanced by elicitation by MJ (in the range 50-400 microM); however, fresh weight, dry weight and growth ratio of the cells was strongly inhibited by increasing MJ concentration. The highest ginsenoside yield was obtained at 200 microM MJ. In the second experiment, 200 microM MJ was added on day 15 during the cultivation. The ginsenoside, Rb group, and Rg group ginsenoside content increased 2.9, 3.7, and 1.6 times, respectively, after 8 days of MJ treatment. Rb group gisnsenosides accumulated more than Rg group ginsenosides. Among Rb group ginsenosides, Rb1 content increased significantly by four times but the contents of Rb2, Rc and Rd increased only slightly. Among Rg group ginsenosides, Rg1 and Re showed 2.3-fold and 3.0-fold increments, respectively, whereas there was only a slight increment in Rf group ginsenosides. These results suggest that MJ elicitation is beneficial for ginsenoside production using 5-l bioreactor cell suspension cultures.

Acetates↗

PubMed2004

Nonlinear ac responses of electro-magnetorheological fluids.

We apply a Langevin model to investigate the nonlinear ac responses of electro-magnetorheological (ERMR) fluids under the application of two crossed dc magnetic (z axis) and electric (x axis) fields and a probing ac sinusoidal magnetic field. We focus on the influence of the magnetic fields which can yield nonlinear behaviors inside the system due to the particles with a permanent magnetic dipole moment. Based on a perturbation approach, we extract the harmonics of the magnetic field and orientational magnetization analytically. To this end, we find that the harmonics are sensitive to the degree of anisotropy of the structure as well as the field frequency. Thus, it is possible to real-time-monitor the structure transformation of ERMR fluids by detecting the nonlinear ac responses.

Journal Article↗

PubMed2004

Nonlinear alternating current responses of dipolar fluids.

The frequency-dependent nonlinear dielectric increment of dipolar fluids in nonpolar fluids is often measured by using a stationary relaxation method in which two electric fields are used: The static direct current (dc) field of high strength causing the dielectric nonlinearity, and the probing alternating current (ac) field of low strength and high frequency. When a nonlinear composite is subjected to a sinusoidal electric field, the electric response in the composite will, in general, consist of ac fields at frequencies of higher-order harmonics. Based on the Fröhlich model, we present a theory to investigate the nonlinear ac responses of dipolar fluids containing both polarizable monomers and dimers. In the case of monomers only, our theory reproduces the known results. We obtain the fundamental, second-, and third-order harmonics of the Fröhlich field by performing a perturbation expansion. The even-order harmonics are induced by the coupling between the ac and dc fields, although the system under consideration has a cubic nonlinearity only. The harmonics of the Fröhlich field can be affected by the field frequency, temperature, dispersion strength, and the characteristic frequency of the dipolar fluid, as well as the dielectric constant of the nonpolar fluid. The results are found to be in agreement with recent experimental observations.

Journal Article↗

PubMed2004

Electrokinetic behavior of two touching inhomogeneous biological cells and colloidal particles: effects of multipolar interactions.

We present a theory to investigate electrokinetic behavior, namely, electrorotation and dielectrophoresis under alternating current (ac) applied fields for a pair of touching inhomogeneous colloidal particles and biological cells. These inhomogeneous particles are treated as graded ones with physically motivated model dielectric and conductivity profiles. The mutual polarization interaction between the particles yields a change in their respective dipole moments, and hence in the ac electrokinetic spectra. The multipolar interactions between polarized particles are accurately captured by the multiple images method. In the point-dipole limit, our theory reproduces the known results. We find that the multipolar interactions as well as the spatial fluctuations inside the particles can affect the ac electrokinetic spectra significantly.

Biophysics↗

PubMed2004

Nonlinear alternating current responses of graded materials.

When a composite of nonlinear particles suspended in a host medium is subjected to a sinusoidal electric field, the electrical response in the composite will generally consist of alternating current (ac) fields at frequencies of higher-order harmonics. The situation becomes more interesting when the suspended particles are graded, with a spatial variation in the dielectric properties. The local electric field inside the graded particles can be calculated by the differential effective dipole approximation, which agrees very well with a first-principles approach. In this work, a nonlinear differential effective dipole approximation and a perturbation expansion method have been employed to investigate the effect of gradation on the nonlinear ac responses of these composites. The results showed that the fundamental and third-harmonic ac responses are sensitive to the dielectric-constant and/or nonlinear-susceptibility gradation profiles within the particles. Thus, by measuring the ac responses of the graded composites, it is possible to perform a real-time monitoring of the fabrication process of the gradation profiles within the graded particles.

Journal Article↗

PubMed2004

Dielectric behaviour of graded spherical cells with an intrinsic dispersion.

The dielectric properties of single-shell spherical cells with an intrinsic dielectric dispersion have been investigated. By means of the dielectric dispersion spectral representation (DDSR) for the Clausius-Mossotti (CM) factor, we express the dispersion strengths as well as the characteristic frequencies of the CM factor analytically in terms of the parameters of the cell model. These analytic expressions enable us to assess the influence of various model parameters on the electrokinetics of cells. Various interesting behaviours have been reported. We extend our considerations to a more realistic cell model with a graded core, which can have spatial gradients in the conductivity and/or permittivity. To this end, we address the effects of a graded profile in a small-gradient expansion in the framework of DDSR.

Cell Movement↗

PubMed2003

Electrorotation in graded colloidal suspensions.

Biological cells can be treated as composites of graded material inclusions. In addition to biomaterials, graded composites are important in more traditional materials science. In this paper, we investigate the electrorotation spectrum of a graded colloidal suspension in an attempt to discuss its dielectric properties. For that, we use the recently obtained differential effective dipole approximation and generalize it for nonspherical particles. We find that variations in the conductivity profile may make the characteristic frequency redshifted and have also an effect on the rotation peak. On the other hand, variations in the dielectric profile may enhance the rotation peak, but do not have any significant effect on the characteristic frequency. In the end, we apply our theory to fit experimental data obtained for yeast cells and find good agreement.

Journal Article↗

PubMed2003

Theory of ac electrokinetic behavior of spheroidal cell suspensions with an intrinsic dispersion.

The dielectric dispersion, dielectrophoretic (DEP), and electrorotational (ER) spectra of spheroidal biological cell suspensions with an intrinsic dispersion in the constituent dielectric constants are investigated. By means of the spectral representation method, we express analytically the characteristic frequencies and dispersion strengths both for the effective dielectric constant and the Clausius-Mossotti factor (CMF). We identify four and six characteristic frequencies for the effective dielectric spectra and CMF, respectively, all of them being dependent on the depolarization factor (or the cell shape). The analytical results allow us to examine the effects of the cell shape, the dispersion strength, and the intrinsic frequency on the dielectric dispersion, DEP, and ER spectra. Furthermore, we include the local-field effects due to the mutual interactions between cells in a dense suspension, and study the dependence of co-field or antifield dispersion peaks on the volume fractions.

Journal Article↗