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D D Do

Publications and source records attributed to D D Do.

At least 19 recordsLinked to original sources
PubMed2005

Adsorption of argon on homogeneous graphitized thermal carbon black and heterogeneous carbon surface.

In this paper we investigate the effects of surface mediation on the adsorption behavior of argon at different temperatures on homogeneous graphitized thermal carbon black and on heterogeneous nongraphitized carbon black surface. The grand canonical Monte Carlo (GCMC) simulation is used to study the adsorption, and its performance is tested against a number of experimental data on graphitized thermal carbon black (which is known to be highly homogeneous) that are available in the literature. The surface-mediation effect is shown to be essential in the correct description of the adsorption isotherm because without accounting for that effect the GCMC simulation results are always greater than the experimental data in the region where the monolayer is being completed. This is due to the overestimation of the fluid-fluid interaction between particles in the first layer close to the solid surface. It is the surface mediation that reduces this fluid-fluid interaction in the adsorbed layers, and therefore the GCMC simulation results accounting for this surface mediation that are presented in this paper result in a better description of the data. This surface mediation having been determined, the surface excess of argon on heterogeneous carbon surfaces having solid-fluid interaction energies different from the graphite can be readily obtained. Since the real heterogeneous carbon surface is not the same as the homogeneous graphite surface, it can be described by an area distribution in terms of the well depth of the solid-fluid energy. Assuming a patchwise topology of the surface with patches of uniform well depth of solid-fluid interaction, the adsorption on a real carbon surface can be determined as an integral of the local surface excess of each patch with respect to the differential area. When this is matched against the experimental data of a carbon surface, we can derive the area distribution versus energy and hence the geometrical surface area. This new approach will be illustrated with the adsorption of argon on a nongraphitized carbon at 87.3 and 77 K, and it is found that the GCMC surface area is different from the BET surface area by about 7%. Furthermore, the description of the isotherm in the region of BET validity of 0.06 to 0.2 is much better with our method than with the BET equation.

Journal Article↗
PubMed2004

Effects of potential models on the adsorption of ethane and ethylene on graphitized thermal carbon black. Study of two-dimensional critical temperature and isosteric heat versus loading.

Adsorption of ethylene and ethane on graphitized thermal carbon black and in slit pores whose walls are composed of graphene layers is studied in detail to investigate the packing efficiency, the two-dimensional critical temperature, and the variation of the isosteric heat of adsorption with loading and temperature. Here we used a Monte Carlo simulation method with a grand canonical Monte Carlo ensemble. A number of two-center Lennard-Jones (LJ) potential models are investigated to study the impact of the choice of potential models in the description of adsorption behavior. We chose two 2C-LJ potential models in our investigation of the (i) UA-TraPPE-LJ model of Martin and Siepmann for ethane and Wick et al. for ethylene and (ii) AUA4-LJ model of Ungerer et al. for ethane and Bourasseau et al. for ethylene. These models are used to study the adsorption of ethane and ethylene on graphitized thermal carbon black. It is found that the solid-fluid binary interaction parameter is a function of adsorbate and temperature, and the adsorption isotherms and heat of adsorption are well described by both the UA-TraPPE and AUA models, although the UA-TraPPE model performs slightly better. However, the local distributions predicted by these two models are slightly different. These two models are used to explore the two-dimensional condensation for the graphitized thermal carbon black, and these values are 110 K for ethylene and 120 K for ethane.

Adsorption↗
PubMed2004

Effect of surface-perturbed intermolecular interaction on adsorption of simple gases on a graphitized carbon surface.

In this paper, we investigate the effect of the solid surface on the fluid-fluid intermolecular potential energy. This modified fluid-fluid interaction energy due to the inducement of a solid surface is used in the grand canonical Monte Carlo (GCMC) simulation of various noble gases, nitrogen, and methane on graphitized thermal carbon black. This effect is such that the effective interaction potential energy between two particles close to surface is less than the potential energy if the solid substrate is not present. With this modification the GCMC simulation results agree extremely well with the experimental data over a wide range of pressures while the simulation results with the unmodified potential energy give rise to a shoulder near the neighborhood of monolayer coverage and the significant overprediction of the second and higher layer coverages. In particular the unmodified GCMC results exhibit very sharp change in those higher layers while the experimental data have a much gradual change in the uptake. We will illustrate this theory with adsorption data of argon, xenon, neon, nitrogen, and methane on graphitized thermal carbon black.

Journal Article↗
PubMed2004

Adsorption of ethylene on graphitized thermal carbon black and in slit pores: a computer simulation study.

In this paper, we studied vapor-liquid equilibria (VLE) and adsorption of ethylene on graphitized thermal carbon black and in slit pores whose walls are composed of graphene layers. Simple models of a one-center Lennard-Jones (LJ) potential and a two-center united atom (UA)-LJ potential are investigated to study the impact of the choice of potential models in the description of VLE and adsorption behavior. Here, we used a Monte Carlo simulation method with grand canonical Monte Carlo (GCMC) and Gibbs ensemble Monte Carlo ensembles. The one-center potential model cannot describe adequately the VLE over the practical range of temperature from the triple point to the critical point. On the other hand, the two-center potential model (Wick et al. J. Phys. Chem. B 2000, 104, 8008-8016) performs well in the description of VLE (saturated vapor and liquid densities and vapor pressure) over the wide range of temperature. This UA-LJ model is then used in the study of adsorption of ethylene on graphitized thermal carbon black and in slit pores. Agreement between the GCMC simulation results and the experimental data on graphitized thermal carbon black for moderate temperatures is excellent, demonstrating that the potential of the GCMC method and the proper choice of potential model are essential to investigate adsorption. For slit pores of various sizes, we have found that the behavior of ethylene exhibits a number of features that are not manifested in the study of spherical LJ particles. In particular, the singlet density distribution versus distance across the pore and the angle between the molecular axis and the z direction provide rich information about the way molecules arrange themselves when the pore width is varied. Such an arrangement has been found to be very sensitive to the pore width.

Journal Article↗
PubMed2004

Multicomponent adsorption on activated carbons under supercritical conditions.

Adsorption of binary mixtures onto activated carbon Norit R1 for the system nitrogen-methane-carbon dioxide was investigated over the pressure range up to 15 MPa. A new model is proposed to describe the experimental data. It is based on the assumption that an activated carbon can be characterized by the distribution function of elements of adsorption volume (EAV) over the solid-fluid potential. This function may be evaluated from pure component isotherms using the equality of the chemical potentials in the adsorbed phase and in the bulk phase for each EAV. In the case of mixture adsorption a simple combining rule is proposed, which allows determining the adsorbed phase density and its composition in the EAV at given pressure and compositions of the bulk phase. The adsorbed concentration of each adsorbate is the integral of its density over the set of EAV. The comparison with experimental data on binary mixtures has shown that the approach works reasonably well. In the case of high-pressure binary mixture adsorption, when only total amount adsorbed was measured, the proposed model allows reliably determining partial amounts of the adsorbed components.

Journal Article↗
PubMed2004

Application of density functional theory to capillary phenomena in cylindrical mesopores with radial and longitudinal density distributions.

In this paper, we applied a version of the nonlocal density functional theory (NLDFT) accounting radial and longitudinal density distributions to study the adsorption and desorption of argon in finite as well as infinite cylindrical nanopores at 87.3 K. Features that have not been observed before with one-dimensional NLDFT are observed in the analysis of an inhomogeneous fluid along the axis of a finite cylindrical pore using the two-dimensional version of the NLDFT. The phase transition in pore is not strictly vapor-liquid transition as assumed and observed in the conventional version, but rather it exhibits a much elaborated feature with phase transition being complicated by the formation of solid phase. Depending on the pore size, there are more than one phase transition in the adsorption-desorption isotherm. The solid formation in finite pore has been found to be initiated by the presence of the meniscus. Details of the analysis of the extended version of NLDFT will be discussed in the paper.

Journal Article↗
PubMed2004

Application of density functional theory to analysis of energetic heterogeneity and pore size distribution of activated carbons.

A new approach based on the nonlocal density functional theory to determine pore size distribution (PSD) of activated carbons and energetic heterogeneity of the pore wall is proposed. The energetic heterogeneity is modeled with an energy distribution function (EDF), describing the distribution of solid-fluid potential well depth (this distribution is a Dirac delta function for an energetic homogeneous surface). The approach allows simultaneous determining of the PSD (assuming slit shape) and EDF from nitrogen or argon isotherms at their respective boiling points by using a set of local isotherms calculated for a range of pore widths and solid-fluid potential well depths. It is found that the structure of the pore wall surface significantly differs from that ofgraphitized carbon black. This could be attributed to defects in the crystalline structure of the surface, active oxide centers, finite size of the pore walls (in either wall thickness or pore length), and so forth. Those factors depend on the precursor and the process of carbonization and activation and hence provide a fingerprint for each adsorbent. The approach allows very accurate correlation of the experimental adsorption isotherm and leads to PSDs that are simpler and more realistic than those obtained with the original nonlocal density functional theory.

Journal Article↗
PubMed2004

[Embolization therapy of an arteriovenous fistula after percutaneous lithotripsy in combination with angioplasty of an ipsilateral kidney arterial stenosis].

We describe successful selective coil embolization therapy in a patient with renal hemorrhage caused by iatrogenic pseudoaneurysm after percutaneous nephrostomy and lithotripsy. In the same session, an incidentally detected severe renal artery stenosis that had caused moderate hypertension was treated by balloon angioplasty. No complications occurred. Coaxial micro-catheter technique and platinum microcoils were used for embolization and allowed targeted occlusion of the bleeding renal artery and preserved the surrounding renal parenchyma. Bleeding was controlled immediately and hematuria disappeared after embolization therapy.

Angioplasty, Balloon↗
PubMed2004

Delay of dialysis in end-stage renal failure: prospective study on percutaneous renal artery interventions.

BACKGROUND: Renal artery stenosis (RAS) is a cause of end-stage renal failure. We studied the effect of percutaneous renal artery intervention (PRI) in patients with advanced, progressive disease at risk for renal failure, hypothesizing a beneficial effect. METHODS: Thirty-nine primary and 14 secondary PRIs were performed on 28 patients with atherosclerotic RAS, serum creatinine >300 micromol/L, and progressive loss of renal function >/=1 year before PRI. Renal function and RA patency were prospectively followed for 12 months after primary and secondary PRI. The intervention's effect on the progressive loss of renal function was calculated by comparing reciprocal slopes of serum creatinine against time before and after PRI. RESULTS: Progression of renal failure slowed significantly following PRI. Mean (+/-SE) slopes of reciprocal serum creatinine values were: 6.69 +/- 0.97 L micromol(-1) day(-1) (x10(-6)) before and 6.76 +/- 3.03 L micromol(-1) day(-1) (x10(-6)) after PRI (P= 0.0007). Fifteen patients (53.5%) showed improvement or stabilization of progressive renal dysfunction. Out of 11 patients expected to become dialysis dependent within one year, 8 (72.7%) experienced an improvement in renal function sufficient to remain dialysis-free. Favorable outcome correlated with a lower creatinine level (P= 0.0137) and a more negative slope of progression (r= 0.49, P= 0.020) at entry. Mortality was 10.7%, and rate of local complications was 7.1%. Deterioration of renal function following PRI was suspected in 17.9% of patients. CONCLUSION: PRI may improve renal function and ultimately delay dialysis in patients with advanced renal failure. Possible advantages must be weighed against the risk of renal failure advancement and high procedure-related complication rate.

Aged↗
PubMed2003

Endovascular stent-grafting for diseases of the descending thoracic aorta.

PRINCIPLES: Endoluminal stent-grafts are emerging as a less invasive alternative to conventional open surgery in the management of descending thoracic aortic dissections and aneurysms. We describe our experience with endovascular stent-grafting in the treatment of thoracic aorta pathology. METHODS: 17 Patients were treated with 23 endovascular stents. The underlying pathology was an atherosclerotic aneurysm verum (n = 5), a type B dissection with contained rupture (n = 3), an intramural haematoma with contained rupture (n = 1) and a false aneurysm of unknown origin (n = 1). One patient had Marfan's syndrome and six patients had a traumatic rupture of the descending aorta. RESULTS: Overall 23 stent-grafts were implanted. In one patient, conversion to an open graft replacement of the descending aorta was necessary. One patient died. In four patients (23.5%) a left carotid-subclavia bypass or transposition was performed to achieve a sufficient neck for the proximal stent-graft landing zone. The postoperative control-CT scans revealed a total of six endoleaks (EL) (four type I, one type II and one type IV). Two patients needed a graft extension in a second operation (4 days and 18 month after the first operation), two EL (one type I and one type II) disappeared after 9 and 18 months, respectively and two EL are still under observation. One patient developed a paresis after conversion to open graft replacement. CONCLUSIONS: A variety of diseases of the descending aorta can be treated by endoluminal stent-grafting, which seems to be a valid alternative to open repair in well selected cases. Mortality and morbidity in our small series were low. Continuous follow-up is mandatory.

Adult↗
PubMed2002

Treatment of renal artery fibromuscular dysplasia with balloon angioplasty: a prospective follow-up study.

OBJECTIVES: to assess restenosis rates and blood pressure response after percutaneous transluminal renal angioplasty (PTRA) in patients treated for fibromuscular dysplastic renal artery stenosis. METHODS: a prospective 12-month follow-up study of 27 patients with 31 treated renal artery stenosis. Follow-up assessment included colour-coded duplex sonography (CCD) of renal arteries, monitoring of blood pressure, antihypertensive medication, and creatinine measurements before discharge and at 3, 6, and 12 months. Primary end point was defined as a haemodynamically significant restenosis >60% assessed by CCD. RESULTS: there was a cumulative 23% restenosis rate at 12 months. Arterial hypertension was cured or improved in 93% of patients immediately after the intervention and remained cured/improved in 74% of patients at 12 months of follow-up. Renal failure present in five patients before PTRA stabilised or improved in all patients. CONCLUSION: although restenosis rate after PTRA in fibromuscular dysplasia is as high as in non-ostial atherosclerotic lesions, there remains a considerable higher therapeutic effect. Profound pressure response and recurrent arterial hypertension with restenosis support the high probability of a renovascular origin of arterial hypertension in this young and otherwise healthy population compared to patients with atherosclerotic renal artery lesions.

Adult↗
PubMed2002

[Low-osmolar gadodiamide as alternative contrast agent for diagnostic angiography and angiographic interventions in patients with renal insufficiency].

PURPOSE: To evaluate the benefit and feasibility of gadolinium contrast agents for intra-arterial use in diagnostic and therapeutic angiography in patients with renal insufficiency. METHODS: In 15 patients with planned peripheral or renal vascular interventions digital subtraction angiography with intra-arterial administration of gadolinium (gadodiamide n = 14, gadolinium-DTPA n = 1) was performed. Gadolinium was used selectively after peripheral catheter placement, mainly as an adjunct to CO2 (n = 12), to assess the distal run-off vessels or to characterize stenotic lesions. RESULTS: In 14 cases gadolinium yielded good or satisfactory results that were superior to those of CO2 angiography in the femoropopliteal region and calf, but also to the aorto-iliac vessels and the renal arteries. A small amount of iodinated contrast media was administered due to insufficient contrast of gadolinium in one patient. Mean serum creatinine level after angiography (295 +/- 167 micromol/l; range 125 - 764 micromol/l) was not significantly different (p >/= 0,37) from the initial level (279 +/- 149 micromol/l; range 143 - 728 micromol/l). CONCLUSION: Gadolinium is a viable alternative contrast agent for digital subtraction angiography and percutaneous transluminal angioplasty in patients with renal insufficiency. It enhances the diagnostic evaluation of stenosis and run-off vessels.

Adult↗
PubMed2000

[Progress in endovascular therapy of peripheral arteries].

Percutaneous transluminal angioplasty introduced by Grüntzig nearly 30 years ago, remains one of the most often performed treatment for peripheral artery disease. Aortoiliac stenoses as well as short femoropopliteal occlusions are particularly prone to PTA approach. Because catheter intervention is not only limited to balloon dilatation but offers a wide variety of treatment, endovascular treatment tends to replace the generic term PTA. Recent progress in this field extend far beyond imaging improvement. They comprise new revascularisation techniques and lesions that were formerly considered to be solely treatable by surgery become curable by endovascular approaches. Combined treatment associating thromboaspiration with embolectomy in case of acute or subacute infrainguinal occlusions as well as low dose infiltration thrombolysis with or without additional PTA represent now first choice therapeutic interventions. The manufacturing of stents or stent-grafts represents one of the greatest breakthrough in the field of endovascular interventions. Stents have significantly improved post PTA patency particularly in the suprainguinal location. Furthermore, stent-grafts represent an attractive alternative to bypass surgery in a selected population, to exclude aortic aneurysm, mainly below the renal arteries. The last but not the least of the progress in the management of patients with peripheral artery disease is the multidisciplinary approach of the vascular problems by the specialist involved in cardiovascular diseases.

Angiography↗
PubMed2000

Diffusion-weighted MRI for monitoring neurovascular interventions.

Carotid stenting is increasingly considered as treatment for carotid artery disease. A reliable noninvasive method is desirable for assessing the safety of the procedure. Diffusion-weighted MRI (DWI) is sensitive to early brain ischaemia which becoming widely available and might therefore serve this purpose. We prospectively studied 19 patients referred for investigation of carotid artery disease by echo-planar whole-brain DWI before and within 24 h of stenting. The images obtained at a high b value were examined by two independent blinded reviewers for new high-signal areas consistent with ischaemia. We found that 15 patients had no new changes after stenting. One patient showed enlargement of a posterior watershed lesion after the procedure, which correlated with an increase in neurological deficit. Three other patients had presumed small embolic infarcts on DWI; two were asymptomatic and one had weakness at the hand that corresponded to an embolic infarct with a lesion on DWI in the hand notch. There were no false- positive or -negative results on DWI, when compared to clinical findings. DWI is thus a new method that can demonstrate neurologically silent or asymptomatic infants. It can be used to help to assess the safety and efficacy of neurovascular intervention.

Adult↗
PubMed2000

The pole-pressure test: an easy alternative in patients with ischemic legs and incompressible arteries.

BACKGROUND: Systolic ankle artery pressure measured classically by cuff-manometry and Doppler ultrasound in patients with severely ischemic legs may be falsely elevated because of impaired compressibility of the arteries. We evaluated a hydrostatic blood pressure or so-called pole pressure test by correlating the ankle artery pressure as well as tcpO2 with the pole pressure. PATIENTS AND METHODS: We enrolled 29 patients (18 male, 11 female, 10 diabetics) with critical leg ischaemia. The pole pressure was obtained by elevating the leg, and measuring the height at which the Doppler signal disappears by means of a calibrated pole (recalculating cm H2O for mmHg). We used an 8 MHz cw-Doppler device. Only pole pressure values up to 70 cm H2O were included. In addition tcpO2 at 45 degrees C was recorded at the forefoot of the same leg. RESULTS: When we included the values of the ten diabetic patients the pole pressure of 57.9 +/- 16.2 mmHg (mean +/- SD) was significantly lower by 40.7 mmHg than the ankle pressure of 98. +/- 38.4 mmHg, p < 0.0001 (paired t-test). Without the diabetics the difference was 33.7 mmHg. The correlation coefficient between pole pressure and ankle pressure was 0.546 including the patients with diabetes, and 0.609 excluding the diabetics. The correlation of tcpO2 with the pole pressure, however, was 0.624 regardless of the inclusion of diabetics, while that between tcpO2 and ankle pressure was only 0.250. CONCLUSIONS: The pole pressure test is an easy, inexpensive and fast method providing a meaningful, quantitative measure independent of the compressibility of the arteries.

Aged↗