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1.
Materials (Basel) ; 17(10)2024 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-38793423

RESUMO

In this study, piezoelectric patches are used as actuators to dampen structural oscillations. Damping oscillations is a significant engineering challenge, and the use of piezoelectric patches in smart structures allows for a reduction in oscillations through sophisticated control methods. This analysis involved H-infinity (H∞) robust analysis. H∞ (H-infinity) control formulation is a robust control design method used to ensure system stability and performance under disturbances. When applied to piezoelectric actuators in smart structures, H∞ control aims to design controllers that are robust to variations in system dynamics, external disturbances, and modeling uncertainties, while meeting specified performance criteria. This study outlines the piezoelectric effects and advanced control strategies. A structural model was created using finite elements, and a smart structural model was analyzed. Subsequently, dynamic loads were applied and oscillation damping was successfully achieved by employing advanced control techniques.

2.
Micromachines (Basel) ; 14(10)2023 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-37893369

RESUMO

One of the uses of Helmholtz resonators is as sound absorbers for room acoustic applications, especially for the low frequency range. Their efficiency is centered around their resonance frequency which mainly depends on elements of their geometry such as the resonator volume and neck dimensions. Incorporating additional necks on the body of a Helmholtz resonator (depending on whether they are open or closed) has been found to alter the resulting resonance frequency. For this study, tunable Helmholtz resonators to multiple resonance frequencies, are proposed and investigated utilizing additional necks. The resonance frequencies of various multi-neck Helmholtz resonators are first modeled with the use of the finite element method (FEM), then calculated with the use of an analytical approach and the results of the two approaches are finally compared. The results of this study show that Helmholtz resonators with multiple resonances at desired frequencies are achievable with the use of additional necks, while FEM and analytical methods can be used for the estimation of the resonance frequencies. Analytical and FEM approach results show a good agreement in cases of small number of additional necks, while the increasing differences in cases of higher neck additions, were attributed to the change in effective length of the necks as demonstrated by FEM. The proposed approach can be useful for tunable sound absorbers for room acoustics applications according to the needs of a space. Also, this approach can be applied in cases of additional tunable air resonances of acoustic instruments (e.g., string instruments).

3.
Micromachines (Basel) ; 14(2)2023 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-36837989

RESUMO

In this study, a new technique is presented for enhancing the vibration suppression of shunted piezoelectrics by using an auxetic composite layer. Finite element models have been created to simulate the dynamic behavior of the piezoelectric composite beam. In particular, 2D FE and 3D FE models have been created by simulating the shunt as a passive controller and their results are compared. Furthermore, a parametric analysis is presented of the circuit elements, i.e., the resistors, inductors, and capacitors and of the auxetic material, i.e., the thickness. It was found that the proposed modification by adding an auxetic layer of a considerable thickness enhances the electromechanical coupling and indirectly influences the vibration control of the whole structure. However, the use of 3D modeling is necessary to study this auxetic enhancement.

4.
Biomacromolecules ; 12(4): 1067-71, 2011 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-21361273

RESUMO

Here we present the first molecular imprinted polymer (MIP) that is able to attenuate the biofilm formation of the opportunistic human pathogen Pseudomonas aeruginosa through specific sequestration of its signal molecule N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C(12)-AHL). The MIP was rationally designed using computational modeling, and its capacity and specificity and that of a corresponding blank polymer toward signal molecule of P. aeruginosa (3-oxo-C(12)-AHL) and its analogue were tested. The biofilm formation in the presence of polymers and without polymers was studied using scanning confocal laser microscopy. Staining with crystal violet dye was used for the quantification of the biofilm formation. A significant reduction of the biofilm growth was observed in the presence of MIP (>80%), which was superior to that of the resin prepared without template, which showed a reduction of 40% in comparison with biofilm, which was grown without polymer addition. It was shown that 3-oxo-C(12)-AHL-specific MIP prevented the development of quorum-sensing-controlled phenotypes (in this case, biofilm formation) from being up-regulated. The developed MIP could be considered as a new tool for the elimination of life-threatening infections in a multitude of practical applications; it could, for example, be grafted on the surface of medical devices such as catheters and lenses, be a component of paints, or be used as a wound adsorbent.


Assuntos
Biofilmes , Polímeros/farmacologia , Pseudomonas aeruginosa/efeitos dos fármacos , Percepção de Quorum , Cromatografia Líquida de Alta Pressão , Espectrometria de Massas , Microscopia Confocal , Modelos Moleculares , Pseudomonas aeruginosa/crescimento & desenvolvimento
5.
Biomacromolecules ; 11(4): 975-80, 2010 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-20230030

RESUMO

A first attempt to attenuate the quorum sensing (QS) of a marine heterotroph microorganism, Vibrio fischeri , using signal molecule-sequestering polymers (SSPs) is presented. A set of rationally designed polymers with affinity toward a signal molecule of V. fischeri , N-(beta-ketocaproyl)-l-homoserine lactone (3-oxo-C6-AHL) was produced. It is reported that computationally designed polymers could sequester a signal molecule of V. fischeri and prevent QS-controlled phenotypes (in this case, bioluminescence) from being up-regulated. It was proven that the attenuation of bioluminescence of V. fischeri was due to sequestration of the signal molecule by specific polymers and not due to the toxicity of polymer or nonspecific depletion of nutrients. The ability to disrupt the bacterial communication using easy to synthesize and chemically inert polymers could provide a new concept for the development of pharmaceuticals and susceptible device coatings such as catheters.


Assuntos
4-Butirolactona/análogos & derivados , Aliivibrio fischeri/fisiologia , Desenho de Fármacos , Medições Luminescentes , Polímeros/química , Polímeros/farmacologia , Percepção de Quorum/efeitos dos fármacos , Vibrioses/tratamento farmacológico , 4-Butirolactona/síntese química , 4-Butirolactona/química , 4-Butirolactona/farmacologia , Biologia Computacional , Polímeros/síntese química , Vibrioses/metabolismo
6.
Artigo em Inglês | MEDLINE | ID: mdl-30148685

RESUMO

The determination of acrylamide in potato products, bakery products and coffee, and the human dietary exposure is reported. The method reported is based on a single extraction step with water, followed by the clean-up of the extract using solid phase extraction columns and finally, the determination of acrylamide using UPLC-MS/MS. The MS/MS detection was carried out using an ESI interface in positive ion mode. Internal calibration was used for the quantification of acrylamide, because of the suppression/enhancement matrix effects due to the complex nature of the samples. The method performance characteristics were determined after spiking blank samples. The mean recoveries in spiked coffee samples, potato chips, breakfast cereals and crispbread ranged from 93% to 99%, with RSDs lower than 5% for both repeatability and reproducibility conditions. The estimated limits of detection and quantification of the method were 10 and 32 µg kg-1, respectively. The method was used for monitoring acrylamide in 406 samples. Acrylamide amounts ranged from <32 to 2450 µg kg-1. A total of 360 samples (89%) were contaminated with acrylamide, but only 14% of the samples exceeded the benchmark levels of the EU legislation. Foods with the highest mean acrylamide amounts were potato crisps (642 µg kg-1), French fries (383 µg kg-1) and biscuits (353 µg kg-1). The mean and 95th percentile acrylamide exposures of adolescents in Cyprus were 0.8 and 1.8 µg kg-1 body weight per day, respectively. The estimated levels of dietary exposure to acrylamide are not of concern with respect to neurotoxicity. However, the margins of exposure (MOEs) indicate a concern for carcinogenicity. Potato fried products (45%), fine bakery ware (21%) and potato chips (14%) contributed the most to overall acrylamide exposure.


Assuntos
Acrilamida/análise , Exposição Dietética/análise , Análise de Alimentos , Contaminação de Alimentos/análise , Pão/análise , Cromatografia Líquida de Alta Pressão , Café/química , Chipre , Grão Comestível/química , Humanos , Lanches , Solanum tuberosum/química , Espectrometria de Massas em Tandem
7.
Eur Cytokine Netw ; 17(2): 137-41, 2006 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-16840033

RESUMO

White coat hypertension (WCH) or isolated clinic hypertension is generally accepted to be a benign condition, although some reports have suggested that it may be associated with an increased cardiovascular event rate or other cardiovascular alterations. It has been previously shown that essential hypertension (EH) is associated with abnormalities in haemostatic/fibrinolytic balance and endothelial function. The aim of our study was to assess the impact of WCH on fibrinolytic balance and endothelial function by measuring plasma levels of plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator antigen (tPA), fibrinogen, and thrombomodulin. These markers were determined in 71 patients with EH, 26 with WCH and 87 normotensive healthy control subjects. The three groups were not different with respect to age, gender, smoking habits, BMI and blood lipids. Subjects with WCH were found to have increased plasma levels of PAI-1, tPA, fibrinogen and thrombomodulin compared to controls, but less compared to hypertensive ones. Our results suggest that WCH may be associated with decreased fibrinolytic potential and endothelial dysfunction, indicating that WCH may not be a completely harmless trait.


Assuntos
Transtornos da Coagulação Sanguínea/sangue , Fibrinólise/fisiologia , Hemostasia/fisiologia , Hipertensão/sangue , Feminino , Fibrinogênio/metabolismo , Humanos , Masculino , Pessoa de Meia-Idade , Inibidor 1 de Ativador de Plasminogênio/sangue , Trombomodulina/sangue , Ativador de Plasminogênio Tecidual/sangue
8.
J Clin Hypertens (Greenwich) ; 7(12): 729-33, 2005 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-16330895

RESUMO

Prehypertension seems to be related to increased cardiovascular risk in healthy subjects, while hypoadiponectinemia and hyperresistinemia may contribute to insulin resistance and accelerated atherogenesis. This study investigated whether plasma levels of adiponectin (known to increase insulin sensitivity) and resistin (a protein possibly involved in inflammatory activities) are affected in healthy individuals with prehypertension, and to compare the findings to those of healthy normotensives matched for age, gender, and body mass index. Twenty-six (14 men and 12 women) healthy individuals with prehypertension (mean age, 52+/-5 years; mean body mass index, 23+/-1.5 kg/m2) and 24 healthy normotensives (13 men and 11 women; mean age 53+/-6 years; body mass index 23.2+/-1.4 kg/m2) were studied. The adiponectin and resistin plasma levels were determined by the enzyme-linked immunosorbent assay method. Plasma resistin levels were significantly higher, while adiponectin plasma levels were significantly lower, in prehypertensive subjects compared with normotensive subjects (10.62+/-3.17 ng/mL vs. 6.72+/-3.15 ng/mL and 6.26+/-2.18 mg/mL vs. 12.12+/-4.8 mg/mL; p < 0.01, respectively). The findings suggest that healthy individuals with prehypertension have significantly higher resistin plasma levels and significantly lower adiponectin plasma levels compared with healthy normotensives. These findings may represent another possible mechanism that may increase the cardiovascular risk in this special group of patients, needing further investigation.


Assuntos
Adiponectina/sangue , Hipertensão/sangue , Resistina/sangue , Índice de Massa Corporal , Doenças Cardiovasculares/etiologia , Estudos de Casos e Controles , Ensaio de Imunoadsorção Enzimática , Feminino , Humanos , Hipertensão/complicações , Hipertensão/diagnóstico , Masculino , Pessoa de Meia-Idade , Análise de Regressão , Fatores de Risco
9.
Am J Hypertens ; 17(10): 911-4, 2004 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-15485753

RESUMO

BACKGROUND: Epidemiologic studies have shown that healthy offspring of hypertensive patients exhibit many features of the metabolic syndrome, such as hyperinsulinemia, insulin resistance, and lipid disorders. Patients with essential hypertension have reduced numbers of insulin receptors. The aim of this study was to examine whether the number of insulin receptors is reduced in the erythrocytes of healthy offspring of hypertensive patients in comparison to the offspring of healthy normotensive subjects. METHODS: The study population consisted of 25 healthy offspring of patients with essential hypertension (group A) and 28 healthy offspring of healthy normotensive individuals (group B). The two groups were matched for sex, age, and body mass index. Systolic blood pressure (SBP) and diastolic blood pressure (DBP), resting heart rate (HR), plasma insulin levels, and human insulin receptor (hINR) number in erythrocytes were determined in each participant. RESULTS: Mean SBP, DBP, and resting HR were significantly higher in group A than in group B (121 +/- 13 v 110 +/- 10 mm Hg, 78 +/- 6 v 73 +/- 8 mm Hg, and 76 +/- 4 v 72 +/- 6 beats/min; P < .01, P < .05, and P < .01, respectively). Plasma insulin levels were significantly higher, whereas hINR density was significantly lower, in group A than in group B (21 +/- 7 v 15 +/- 6 pIU/mL, P < .01, and 5.6 +/- 1.4 v 6.8 +/- 1.3 receptors x 10(3)/red cell, P < .01, respectively). CONCLUSIONS: Our findings suggest that increased SBP, DBP, HR, plasma insulin levels, and decreased erythrocyte hINR density preexist in healthy offspring of patients with essential hypertension.


Assuntos
Filho de Pais com Deficiência , Eritrócitos/metabolismo , Hipertensão/genética , Receptor de Insulina/sangue , Adolescente , Pressão Sanguínea , Estudos de Casos e Controles , Feminino , Frequência Cardíaca , Humanos , Insulina/sangue , Masculino
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