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Xinhua Hu

Publications and source records attributed to Xinhua Hu.

15 recordsLinked to original sources
PubMed2026

Direct background subtraction LC-MS/MS assay for human plasma progesterone: Full validation and comparative application.

OBJECTIVE: To develop and validate a liquid chromatography-tandem mass spectrometry method based on direct background subtraction for the quantification of endogenous progesterone in human plasma. METHODS: Protein precipitation was used for sample preparation with deuterated progesterone as the internal standard. Chromatographic separation was performed on an ACQUITY C18 column using gradient elution with 0.1% formic acid in water and acetonitrile at a flow rate of 0.3 mL/min. Mass spectrometry was operated in positive electrospray ionization mode with multiple reaction monitoring. Instead of using analyte-stripped matrix or surrogate matrix, authentic plasma was directly used for all validation experiments. Quantitation was achieved by subtracting the background signal, and results were compared with those from the classical method using stripped matrix. RESULTS: Excellent linearity was achieved over 0.1-100 ng/mL (R2 ≥ 0.99). Precision, accuracy, recovery, matrix effect, and stability all met FDA and ICH M10 acceptance criteria. Compared with the classical method, the bias in Cmax and AUC0-t was within ±15%, indicating no significant difference between the two methods. CONCLUSION: The direct background subtraction method avoids laborious preparation of blank matrix, eliminates matrix effect discrepancies, and is simple, efficient, and low-cost. It can serve as a general strategy for endogenous substance determination.

Humans↗
PubMed2006

Higher-order incidence transfer matrix method used in three-dimensional photonic crystal coupled-resonator array simulation.

The plane-wave-based transfer matrix method with rational function interpolation and higher-order plane-wave incidence is proposed as an efficient calculation approach to simulate three-dimensional photonic crystal devices. As an example, the dispersion relations and quality factors are calculated for resonant cavity arrays embedded in a woodpile photonic crystal. An interesting ultraslow negative group velocity is observed in this structure.

Journal Article↗
PubMed2006

Diamagnetic response of metallic photonic crystals at infrared and visible frequencies.

We show analytically and numerically that diamagnetic response (effective magnetic permeability mue<1) at infrared and visible frequencies can be achieved in photonic crystals composed of metallic nanowires or nanospheres when the wavelength is much larger than the lattice constant a (lambda approximately 2000a). When lambda approximately100a, the metallic photonic crystals will exhibit strong diamagnetic response (mue<0.8), leading to many interesting phenomena such as the unusual Brewster angle for s waves and incident-angle-and-polarization-independent reflection and transmission.

Journal Article↗
PubMed2006

Omnidirectional total reflection for liquid surface waves propagating over a bottom with one-dimensional periodic undulations.

We study theoretically the propagation of liquid surface waves over a bottom with one-dimensional (1D) periodic undulations. We find a general criterion for omnidirectional total reflection in such a system. Numerical simulations based on a transfer matrix method demonstrate unambiguously the existence of omnidirectional total reflection for liquid surface waves propagating over a bottom with 1D periodic undulations.

Journal Article↗
PubMed2006

Anomalous Doppler effects in phononic band gaps.

Doppler effects in periodic acoustic media were studied theoretically and experimentally. Analytical formulas are derived using the Green's function formalism. We found that a far field observer cannot hear the sound inside a band gap from a stationary source, but a moving source can be heard even if the frequency is inside the gap, and the Doppler shifts can be inverted or anomalously large.

Journal Article↗
PubMed2005

Refraction of water waves by periodic cylinder arrays.

We show that in the long wavelength limit, water waves propagate through an array of bottom-mounted vertical cylinders as if the water has an effective depth and effective gravitational constant that depends on the filling ratio of the cylinders, leading to refraction phenomena that can be described by analytic formulas. The results are obtained with rigorous homogenization techniques, as well as the multiple scattering formalism that gives full dispersion relationships. This phenomenon provides a mechanism to control the flow of ocean wave energy, as exemplified by a water-wave focusing lens.

Journal Article↗
PubMed2005

Two-dimensional sonic crystals with Helmholtz resonators.

We present a type of sonic crystal composed with an array of two-dimensional Helmholtz resonators, which in the long-wave regime have both a high relative acoustic refractive index n and at the same time, a small acoustic impedance Z mismatch with air for airborne sound. We analyze the n and Z of such sonic crystals by finite-difference time-domain simulations, and by mapping our results to a corresponding electromagnetic (EM) model, and we find that our Helmholtz resonant sonic crystal has a bigger effective magnetic permeability mu than the conventional rigid-cylinder sonic crystal in its EM counterpart. As a result, a thin convergent lens with very good focusing effect is demonstrated based on our crystal.

Journal Article↗
PubMed2005

NT3 inhibits FGF2-induced neural progenitor cell proliferation via the PI3K/GSK3 pathway.

Neurotrophin 3 (NT3), a member of the neurotrophin family, antagonizes the proliferative effect of fibroblast growth factor 2 (FGF2) on cortical precursors. However, the mechanism by which NT3 inhibits FGF2-induced neural progenitor (NP) cell proliferation is unclear. Here, using an FGF2-dependent rat neurosphere culture system, we found that NT3 inhibits both FGF2-induced neurosphere growth and bromodeoxyuridine (BrdU) incorporation in a dose-dependent manner. U0126, a mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor, and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, both inhibited FGF2-induced BrdU incorporation, suggesting that the extracellular signal-regulated kinase1/2 (ERK1/2) and PI3K pathways are required for FGF2-induced NP cell proliferation. NT3 significantly inhibited FGF2-induced phosphorylation of Akt and glycogen synthase kinase 3beta (GSK3beta), a downstream kinase of Akt, whereas phosphorylation of ERK1/2 was unaffected. The inhibitory effect of NT3 on FGF2-induced NP cell proliferation was abolished by LY294002, and treatment with SB216763, a specific GSK3 inhibitor, antagonized the NT3 effect, rescuing both neurosphere growth and BrdU incorporation. Moreover, experiments with anti-NT3 antibody revealed that endogenous NT3 also plays a role in inhibiting FGF2-induced NP cell proliferation, and that anti-NT3 antibody enhanced phospho-Akt and phospho-GSK3beta levels in the presence of FGF2. These findings indicate that FGF2-induced NP cell proliferation is inhibited by NT3 via the PI3K/GSK3 pathway.

Animals↗
PubMed2004

Superlensing effect in liquid surface waves.

We present experimental observations and numerical simulations of superlensing effect in liquid surface waves. We use rigid cylinders to create a two-dimensional periodic lattice, in which liquid surface waves propagate. Through the observation of a superlensing effect, we demonstrate the existence of negative refraction in surface waves. In addition, a complete band gap is found.

Journal Article↗
PubMed2004

Erk1/2 but not PI3K pathway is required for neurotrophin 3-induced oligodendrocyte differentiation of post-natal neural stem cells.

Neurotrophin 3 (NT3) induces mouse cortical stem cells to an asymmetric division from a symmetric division, suggesting that NT3 may work as an early differentiative signal for neural stem cells (NSCs). Here, using cultured post-natal hippocampal stem cells as a model, we demonstrated that NT3-stimulation causes NSCs to differentiate into oligodendrocyte precursors (OLPs) through an extracellular signal-related kinase1/2 (Erk1/2)-dependent pathway. Following the treatment of NT3 for 24 h, NSCs differentiated into more OLPs and fewer neurons, whereas the proliferation and survival of OLPs were not affected. NT3 induced a series of intracellular responses including enhancement of phosphorylation of Erk1/2 or Akt and increase of expression of oligodendrocyte lineage gene (Olig)-1, a transcriptional factor known to participate in oligodendrocyte development. Application of U0126, a specific inhibitor of MEK1/2 which are upstream to Erk1/2, blocked the phosphorylation of Erk1/2, suppressed the expression of Olig-1 and prevented NSC differentiation into OLPs in response to NT3 stimulation. Blockade of TrkC also inhibited the differentiation of NSCs to OLPs induced by NT3. However, administration of LY294002, an inhibitor of phosphatidylinositol 3 kinase (PI3K), blocked the phosphorylation of Akt but did not affect the effect of NT3 on the expression of Olig-1 and on NSC differentiation into OLPs. Taken together, these results suggest that NT3 induce NSCs to differentiate into OLPs by enhancing the expression of Olig-1 through an Erk1/2-dependent pathway.

Animals↗
PubMed2003

Complete band gaps for liquid surface waves propagating over a periodically drilled bottom.

A plane-wave expansion approach is developed to solve the mild-slope equation for liquid surface waves propagating over a bottom with periodic structures. Band structures are calculated for the bottom periodically drilled with the square or triangular lattice of holes. Complete band gaps are found for both lattices. Parameters that influence the formation of band gaps are discussed.

Journal Article↗
PubMed2003

Coloration strategies in peacock feathers.

We report the mechanism of color production in peacock feathers. We find that the cortex in differently colored barbules, which contains a 2D photonic-crystal structure, is responsible for coloration. Simulations reveal that the photonic-crystal structure possesses a partial photonic bandgap along the direction normal to the cortex surface, for frequencies within which light is strongly reflected. Coloration strategies in peacock feathers are very ingenious and simple: controlling the lattice constant and the number of periods in the photonic-crystal structure. Varying the lattice constant produces diversified colors. The reduction of the number of periods brings additional colors, causing mixed coloration.

Animals↗
PubMed2002

[The gene expression of nuclear transcriptional factor-kappa B and I kappa B in autogenous vein graft in rats].

OBJECTIVE: To investigate the gene expression of nuclear transcriptional factor-kappa B (NF-kappa B) p65 and its inhibiting factor I kappa B in autogenous vein graft. METHODS: The right common jugular vein was transplanted to infrarenal abdominal aorta by microsurgical technique among 80 Wistar rats so as to establish an autogenous vein graft model. Ten vein graft samples were harvested 6 hours, 24 hours, 3 days, 7 days, 2 weeks, 4 weeks, 6 weeks, and 8 weeks after surgery. NF kappa B p65 mRNA and I kappa B beta mRNA were measured by reverse transcription-PCR and in situ hybridization. Western blotting and immunohistochemistry were used to detect the protein expression of NF kappa B p65 and I kappa B. RESULTS: The expressions of NF kappa B p65 mRNA and I kappa B beta mRNA 6 hours after the surgery were 16% +/- 4% and 31% +/- 9% respectively (P < 0.01 vs. control vein). The expression of NF kappa B p65 mRNA reached in peak during the period 3 days to 7 days after the surgery (37% +/- 12% and 34% +/- 10% respectively, P< 0.01 vs. other teams), however, the I kappa B beta mRNA expression reached its peak during 1 to 2 weeks after the surgery (53% +/- 17% and 49% +/- 10% respectively, P < 0.01 vs. other teams). The expressions of NF kappa B p65 mRNA and I kappa B beta mRNA recovered to their baseline values 6 weeks after surgery. The expression of p65 protein reached its peak 1 week after the surgery (32% +/- 13%) and then decreased gradually. The expressions of I kappa B alpha and I kappa B beta decreased to 1/3 to 1/2 of the normal vein 6 hours to 24 hours after the surgery and then increased to 5 times that of the control vein 2 weeks after surgery (35% +/- 11% and 44% +/- 13% respectively). CONCLUSION: The NF-kappa B/I kappa B system is activated in autogenous vein graft. The NF kappa B may become a new target for the prevention and therapy of intimal hyperplasia and stenosis after vein graft.

Animals↗