Biomedical subjects

C-H Lai

Publications and source records attributed to C-H Lai.

11 recordsLinked to original sources

PubMed2005

Phase synchronization of a pair of spiral waves.

The interaction of a pair of spiral waves with different independent rotation frequencies is studied. In a very large frequency mismatch searching region, we observe three different pattern formation phenomena: (a) phase-synchronization-induced invasion under a relatively small frequency mismatch, i.e., the spiral wave with slower frequency (longer period) is swept away by a traveling wave, which is induced and phase synchronized by the faster spiral wave; (b) the coexistence of two spiral waves at sufficiently large parameter mismatch; and (c) an intermediate state, a non-phase-synchronous invasion, that is, similarly the slower spiral wave is swept by an approximate planar wave, whose frequency, however, is intermediate between those of the faster and slower waves. A point-source model is studied to analyze all these phenomena in a unified way.

Journal Article↗

PubMed2005

Bistable chaos without symmetry in generalized synchronization.

Frequently, multistable chaos is found in dynamical systems with symmetry. We demonstrate a rare example of bistable chaos in generalized synchronization (GS) in coupled chaotic systems without symmetry. Bistable chaos in GS refers to two chaotic attractors in the response system which both synchronize with the driving dynamics in the sense of GS. By choosing appropriate coupling, the coupled system could be symmetric or asymmetric. Interestingly, it is found that the response system exhibits bistability in both cases. Three different types of bistable chaos have been identified. The crisis bifurcations which lead to the bistability are explored, and the relation between the bistable attractors is analyzed. The basin of attraction of the bistable attractors is extensively studied in both parameter space and initial condition space. The fractal basin boundary and the riddled basin are observed and they are characterized in terms of the uncertainty exponent.

Journal Article↗

PubMed2005

Effects of surface electrical stimulation on the muscle-tendon junction of spastic gastrocnemius in stroke patients.

PURPOSE: The purpose of this study was to explore the effects of spasticity suppression by surface electrical stimulation (ES) o the muscle-tendon junction of spastic gastrocnemius muscles in stroke. METHODS: Twenty-four neurologically stable stroke patients (aged 41-69 years, 12-35 months post-stroke), with spasticity graded 2 or 3 on the modified Ashworth scale, were recruited and divided into two groups. In the ES group, each patient received 20 min of surface ES once daily, 6 days per week for 1 month. In the control groups, ES was used with stimulation intensity kept at zero. To evaluate the therapeutic effect, the modified Ashworth scale, Fmax/Mmax ratio, H-reflex latency, H-reflex recovery curve, and the 10-m walking time were tested before and after the 1-month of treatment. RESULTS: In the ES group, the modified Ashworth scale showed a trend toward reduced spasticity after 1 month of treatment. The Fmax/Mmax ratio decreased from 8.10% +/- 4.84% to 4.00% +/- 1.36%; the H-reflex latency increased from 28.87 +/- 2.45 ms to 29.40 +/- 2.57 ms; the H-reflex recovery curves indicated a downward shift; and the 10-metre walking time significantly decreased after ES. In the control group, none of the measures showed a statistically significant change. CONCLUSIONS: In this study, we demonstrated a way to suppress spasticity at a metameric site and to increase walking speed effectively by applying surface ES on the muscle-tendon junction of spastic gastrocnemius muscles.

Adult↗

PubMed2005

p53 polymorphisms associated with mutations in and loss of heterozygosity of the p53 gene in male oral squamous cell carcinomas in Taiwan.

The present study was designed to examine whether different p53 haplotypes of exon 4-intron 3-intron 6 affect the frequency of mutations and loss of heterozygosity (LOH) of the p53 gene in male oral squamous cell carcinomas (OSCCs) in Taiwan. We found that individuals without two Pro-W-G alleles had significantly higher frequency of p53 mutations than those with two Pro-W-G alleles (odds ratio (OR) = 1.98; 95% confidence interval (CI), 1.10-3.56). Out of the 172 p53 gene exon 4 informative male OSCCs, 72 (41.9%) showed LOH. Among these 72 OSCCs with LOH, the frequency of Pro allele loss was 73.6% (53/72). It is notable that alcohol drinking increased the frequency of Arg allele loss (OR = 10.56; 95% CI, 1.23-234.94) in OSCCs from patients who both smoked cigarettes and chewed areca quid (AQ). The frequency of LOH of p53 was not different between p53-mutated OSCCs and p53-normal OSCCs. Thus, the present study revealed that (a) the Arg allele is associated with p53 mutations, (b) the Pro allele is preferentially lost in OSCCs associated with cigarette smoking and AQ chewing, while the frequency of Arg allele loss is increased with alcohol drinking, and (c) haploinsufficiency of p53 is in itself likely to contribute to tumour progression in Taiwanese OSCCs.

Adult↗

PubMed2005

Exposure to traffic exhausts and oxidative DNA damage.

AIMS: To assess the relations between exposure to traffic exhausts and indicators of oxidative DNA damage among highway toll station workers. METHODS: Cross-sectional study of 47 female highway toll station workers exposed to traffic exhausts and 27 female office workers as a reference group. Exposure assessment was based on average and cumulative traffic density and a biomarker of exposure, urinary 1-hydroxypyrene-glucuronide (1-OHPG). Urinary 8-hydroxydeoxyguanosine (8-OHdG) was used as a biomarker of oxidative DNA damage. Plasma nitric oxide (NO) was measured as an indicator of oxidative stress related to traffic exhaust exposure. RESULTS: The mean concentration of urinary 8-OHdG was substantially higher among the exposed non-smokers (13.6 microg/g creatinine) compared with the reference non-smokers (7.3 microg/g creatinine; difference 6.3, 95% CI 3.0 to 9.6). The mean concentration of NO among the exposed (48.0 micromol/l) was also higher compared with the reference non-smokers (37.6 micromol/l; difference 10.4, 95% CI -0.4 to 21.2). In linear regression adjusting for confounding, a change in log(8-OHdG) was statistically significantly related to a unit change in log(1-OHPG) (beta = 0.372, 95% CI 0.081 to 0.663). CONCLUSIONS: Results indicate that exposure to traffic exhausts increases oxidative DNA damage. Urinary 8-OHdG is a promising biomarker of traffic exhaust induced oxidative stress.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2004

Controllability of flow turbulence.

In this paper, we study the controllability of real-world flow turbulence governed by the two-dimensional Navier-Stokes equations, using strategies developed in chaos control. A case of control/synchronization of turbulent dynamics is observed when only one component of the velocity field vector is unidirectionally coupled to a target state, while the other component is uncoupled. Unlike previous results, it is shown that the dynamics of the whole velocity field cannot be completely controlled/synchronized to the target, even in the limit of long time and strong coupling strength. It is further revealed that the controlled component of the velocity field can be fully controlled/synchronized to the target, but the other component, which is not directly coupled to the target, can only be partially controlled/synchronized to the target. By extending an auxiliary method to distributed dynamic systems, the partial synchronization of two turbulent orbits in the present study can be categorized in the domain of generalized synchronization of spatiotemporal dynamics.

Journal Article↗

PubMed2004

Error function attack of chaos synchronization based encryption schemes.

Different chaos synchronization based encryption schemes are reviewed and compared from the practical point of view. As an efficient cryptanalysis tool for chaos encryption, a proposal based on the error function attack is presented systematically and used to evaluate system security. We define a quantitative measure (quality factor) of the effective applicability of a chaos encryption scheme, which takes into account the security, the encryption speed, and the robustness against channel noise. A comparison is made of several encryption schemes and it is found that a scheme based on one-way coupled chaotic map lattices performs outstandingly well, as judged from quality factor.

Algorithms↗

PubMed2003

Complete synchronization and generalized synchronization of one-way coupled time-delay systems.

The complete synchronization and generalized synchronization (GS) of one-way coupled time-delay systems are studied. We find that GS can be achieved by a single scalar signal, and its synchronization threshold for different delay times shows the parameter resonance effect, i.e., we can obtain stable synchronization at a smaller coupling if the delay time of the driven system is chosen such that it is in resonance with the driving system. Near chaos synchronization, the desynchronization dynamics displays periodic bursts with the period equal to the delay time of the driven system. These features can be easily applied to the recovery of time-delay systems.

Journal Article↗

PubMed2002

Tailoring wavelets for chaos control.

Chaos is a class of ubiquitous phenomena and controlling chaos is of great interest and importance. In this Letter, we introduce wavelet controlled dynamics as a new paradigm of dynamical control. We find that by modifying a tiny fraction of the wavelet subspaces of a coupling matrix, we could dramatically enhance the transverse stability of the synchronous manifold of a chaotic system. Wavelet controlled Hopf bifurcation from chaos is observed. Our approach provides a robust strategy for controlling chaos and other dynamical systems in nature.

Journal Article↗

PubMed2002

Transition from intermittency to periodicity in lag synchronization in coupled Rössler oscillators.

The dynamical and statistical behavior of lag synchronization in two coupled self-sustained chaotic Rössler oscillators is reexamined. The lack of uniqueness in the conventional characterization of lag synchronization based on the similarity function has caused much skepticism about the existence of lag synchronization. We provide an evidence that the emergence of lag synchronization is associated with the transition from on-off intermittency to a periodic structure in the laminar phase distribution.

Journal Article↗

PubMedDate not supplied

Prognostic value of age and histologic type in neoadjuvant chemotherapy plus radical surgery for bulky (>/=4 cm) stage IB and IIA cervical carcinoma.

The purpose of this study was to investigate pretreatment variables related to prognosis and to evaluate long-term outcome in patients with bulky early-stage cervical carcinoma who were enrolled into a protocol treatment of neoadjuvant chemotherapy (NAC) followed by radical surgery. Between 1988 and 1999, 162 women with previously untreated bulky (>/=4 cm) stage IB or IIA carcinoma of the uterine cervix registered to receive cisplatin, vincristine, and bleomycin for three cycles followed by radical hysterectomy and pelvic lymphadenectomy, were enrolled into this study. The 5-year relapse-free (RFS) and overall survival (OS) rates of the whole series were 65% and 69%, respectively. In multivariate analyses, age (< 35 vs. >/= 35-year-old: relative risk [RR], 2.06; 95% confidence interval [CI], 1.02-4.14; P = 0.043) and histologic type (adeno-adenosquamous vs. squamous carcinoma: RR, 2.60; 95% CI, 1.26-5.39; P = 0.010) were independent variables associated with RFS, and age (< 35 vs. >/= 35-year-old: RR, 2.53; 95% CI, 1.24-5.14; P = 0.010) and pre-NAC tumor size (> 5 vs. = 5 cm: RR, 2.06; 95% CI, 1.09-3.90; P = 0.027) were significantly related to OS. Narrowing down patient selection to squamous carcinoma and age older than 35 years with stratification of tumor size (break point of 5 cm) is recommended in future trials involving cisplatin-based NAC plus radical surgery.

Adult↗