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J Hafner

Publications and source records attributed to J Hafner.

At least 19 recordsLinked to original sources
PubMed2006

Ab initio based tight-binding molecular dynamics simulation of the sticking and scattering of O2Pt(111).

The sticking and scattering of O(2)Pt(111) has been studied by tight-binding molecular dynamics simulations based on an ab initio potential energy surface. We focus, in particular, on the sticking probability as a function of the angle of incidence and the energy and angular distributions in scattering. Our simulations provide an explanation for the seemingly paradox experimental findings that adsorption experiments suggest that the O(2)Pt(111) interaction potential should be strongly corrugated while scattering experiments indicate a rather small corrugation. The potential energy surface is indeed strongly corrugated which leads to a pronounced dependence of the sticking probability on the angle of incidence. The scattered O(2) molecules, however, experience a rather flat surface due to the fact that they are predominantly scattered at the repulsive tail of the potential.

Journal Article↗
PubMed2006

[The role of surgery in the treatment of acne scars].

Severe acne lead to inesthetic scars on the face of young adults. A new classification based on the morphology of acne scars allows to establish the more appropriate therapeutic strategy. The surgical technics are: punch-excision, punch-elevation, subcission, dermal graft or adipose tissue autotransplantation. Skin resurfacing by dermabrasion, CO2 or Erbium/YAG laser or laser remodeling could be performed as a complement of the surgery. By associating these treatments acne scars are greatly improved.

Acne Vulgaris↗
PubMed2005

A density functional theory study of molecular and dissociative adsorption of H2 on active sites in mordenite.

Adsorption and chemisorption of H2 in mordenite is studied using ab initio density functional theory (DFT) calculations. The geometries of the adsorption complex, the adsorption energies, stretching frequencies, and the capacity to dissociate the adsorbed molecule are compared for different active sites. The active centers include a Brønsted acid site, a three-coordinated surface Al site, and Lewis sites formed by extraframework cations: Na+, Cu+, Ag+, Zn2+, Cu2+, Ga3+, and Al3+. Adsorption properties of cations are compared for a location of the cation in the five-membered ring. This location differs from the location in the six-membered ring observed for hydrated cations. The five-membered ring, however, represents a stable location of the bare cation. In this position any cation exhibits higher reactivity compared with the location in the six-membered ring and is well accessible by molecules adsorbed in the main channel of the zeolite. Calculated adsorption energies range from 4 to 87 kJ/mol, depending on electronegativity and ionic radius of the cation and the stability of the cation-zeolite complex. The largest adsorption energy is observed for Cu+ and the lowest for Al3+ integrated into the interstitial site of the zeolite framework. A linear dependence is observed between the stretching frequency and the bond length of the adsorbed H2 molecule. The capacity of the metal-exchanged zeolite to dissociate the H2 molecule does not correlate with the adsorption energy. Dissociation is not possible on single Cu+ cation. The best performance is observed for the Ga3+, Zn2+, and Al3+ extraframework cations, in good agreement with experimental data.

Journal Article↗
PubMed2005

Periodic DFT calculations of the stability of Al/Si substitutions and extraframework Zn2+ cations in mordenite and reaction pathway for the dissociation of H2 and CH4.

The local stability of Al atoms replacing Si in the zeolite framework is compared for all inequivalent tetrahedral (T) sites in mordenite. For Al/Si substitutions in two T sites the stable location of the compensating extraframework Zn(2+) cation forming a Lewis acid site is determined. In the most stable Zn-MOR structures Zn(2+) is located in a small ring (5MR, 6MR) containing two Al/Si substitutions. In less stable structures the Al atoms are placed at larger distances from each other and Zn(2+) interacts with only one Al site. The simulated adsorption of H(2) and CH(4) shows that adsorption strength decreases with increasing stability of the Zn(2+) Lewis site. A higher adsorption strength is observed for Zn(2+) deposited in the 5MR than for the 6MR. The reactivity of a series of stable Zn(2+) Lewis sites is tested via the dissociative adsorption of H(2) and CH(4). The heterolytic dissociation of the adsorbed molecule on the extraframework Zn(2+) cation produces a proton and an anion. The anion binds to Zn(2+) and proton goes to the zeolite framework, restoring a Brønsted acid site. Because bonding of the anion to Zn(2+) is almost energetically equivalent for Zn(2+) in any of the extraframework positions the dissociation is governed by stabilizing bonding of the proton to the framework. Those structures which can exothermically accommodate the proton represent reaction pathways. Due to the repulsion between the proton and Zn(2+) the most favorable proton-accepting O sites are not those of the ring where Zn(2+) is deposited, but O sites close to the ring. Large differences are observed for neighboring positions in a- and b-directions and those oriented along the c-vector. Finally, among the stable Zn(2+) Lewis sites not all represent reaction pathways for dehydrogenation. For all of them the dissociation of H(2) is an exothermic process. In structures exhibiting the highest reactivity the Al/Si substitutions are placed at a large distance and the Zn(2+) cation interacts with O-atoms next to Al in the T4 site of the 5MR. This Lewis site is strong enough to break the C-H bond in the CH(4) molecule.

Journal Article↗
PubMed2005

Ab initio density-functional study of the bridging addition of acrylonitrile on the Si(100) surface.

Acrylonitrile may react with the Si(100) surface in a number of ways. Fifteen different configurations have been identified. This study which complements an earlier study devoted to cycloadditions and bonds involving a single atom deals essentially with configurations involving cumulative double bonds. Factors affecting the relative stability of various mesomeric forms are shown to be the proximity to tetrahedral geometry and the compatibility of the dipole form with buckled structures. Tripods are shown to be a way to accommodate a priori unfavorable structures.

Journal Article↗
PubMed2005

Theoretical investigation of CO interaction with copper sites in zeolites: periodic DFT and hybrid quantum mechanical/interatomic potential function study.

Periodic DFT and combined quantum mechanics/interatomic potential function (QM-pot) models were used to describe the interaction of CO with the Cu+ sites in FER. The CO stretching frequencies were calculated using omega(CO)(CCSD(T))/r(CO)(DFT) scaling method relating frequencies determined using a high-level quantum-chemical (coupled clusters) method for simple model carbonyls to CO bond lengths calculated using periodic DFT and QM-pot methods for the Cu+-zeolite system. Both periodic DFT and QM-pot models together with omega(CO)/r(CO) scaling describe the CO stretching dynamics with the "near spectroscopic accuracy", giving nu(CO) = 2156 cm(-1) in excellent agreement with experimental data. Calculations for various Cu+ sites in FER show that both types of Cu+ sites in FER (channel-wall sites and intersection sites) have the same CO stretching frequencies. Thus, the CO stretching frequencies are not site-specific in the CO/Cu+/FER system. The convergence of the results with respect to the model size was analyzed. When the same exchange-correlation functional is used the adsorption energies from periodic DFT and QM-pot are in good agreement (about 2 kcal/mol difference) but substantially larger than those of the experiment. The adsorption energy calculated with the B3LYP functional agrees with available experimental data. The overestimation of the adsorption energy in DFT calculations (periodic or QM-pot) is related to a red-shift of the CO stretching mode, both result from an underestimation of the HOMO(5sigma)-LUMO(2pi) gap of CO and the consequent overestimation of the Cu(+)(d)-CO(2pi*) back-donation. For the adsorption energy, this can be overcome by the use of hybrid B3LYP exchange-correlation functional. For the frequency calculations, the DFT problem can be overcome by the use of the omega(CO)(CCSD(T))/r(CO)(DFT) correlation.

Carbon Monoxide↗
PubMed2005

Adsorption and vibrational spectroscopy of CO on mordenite: Ab initio density-functional study.

We present a periodic density-functional investigation of the adsorption and the vibrational spectroscopy of CO in mordenite. Our results highlight a pronounced sensitivity of the strength of the hydrogen bond between the acidic hydroxyl groups and the adsorbed molecule, and hence of the induced red shift of the OH, and the blue shift of the CO stretching mode on the choice of the exchange-correlation functional. The popular Perdew-Wang (PW) gradient-corrected functional strongly overestimates the frequency shifts and the interaction energies. We demonstrate that the revised Perdew-Burke-Ernzerhof (RPBE) functional leads to an improved description of hydrogen bonding. For bridging OH groups, terminal silanol groups and for Lewis sites formed by tricoordinated Al atoms, we predict adsorption energies and frequency shifts in good agreement with experiment. The calculated difference in the binding energies of CO in purely siliceous mordenite and at Brønsted acid sites in the main channel agrees very well with microcalorimetry data. We find that Brønsted acid sites in the small channels (the side-pockets) of mordenite do not adsorb CO, which is adsorbed only in the main channel via the C atom. For these adsorption complexes we find reasonable (though not perfect) agreement of the predicted blue shift of the CO-mode and of the red shift of the OH-mode with experiment. Our prediction that the side-pockets are inaccessible to CO correlates well with the microcalorimetric studies and with experimental observation of the adsorption of O(2), N(2) and H(2) molecules but contradicts the current interpretation of experimental adsorption studies for CO.

Journal Article↗
PubMed2004

Adsorption and vibrational spectroscopy of ammonia at mordenite: ab initio study.

The adsorption of ammonia at various active centers at the outer and inner surfaces of mordenite, involving Brønsted acid (BA) sites, terminal silanol groups, and Lewis sites has been investigated using periodic ab initio density-functional theory. It is shown that ammonia forms an ammonium ion when adsorbed at strong BA sites. The calculated adsorption energies for different BA sites vary in the interval from 111.5 to 174.7 kJ/mol depending on the local environment of the adduct. The lowest adsorption energy is found for a monodentate complex in the main channel, the highest for a tetradentate configuration in the side pocket. At weak BA sites such as terminal silanol groups or a defect with a BA site in a two-membered ring ammonia is H bonded via the N atom. Additional weak H bonds are formed between H atoms of ammonia and O atoms of neighboring terminal silanol groups. The calculated adsorption energies for such adducts range between 61.7 and 70.9 kJ/mol. The interaction of ammonia with different Lewis sites is shown to range between weak (DeltaE(ads)=17.8 kJ/mol) and very strong (DeltaE(ads)=161.7 kJ/mol), the strongest Lewis site being a tricoordinated Al atom at the outer surface. Our results are in very good agreement with the distribution of desorption energies estimated from temperature-programmed desorption (TPD) and microcalorimetry experiments, the multipeaked structure of the TPD spectra is shown to arise from strong and weak Brønsted and Lewis sites. The vibrational properties of the adsorption complexes are investigated using a force-constant approach. The stretching and bending modes of NH(4) (+) adsorbed to the zeolite are strongly influenced by the local environment. The strongest redshift is calculated for the asymmetric stretching mode involving the NH group hydrogen bonded to the bridging O atom of the BA site, the shift is largest for a monodentate and smallest for a tetradentate adsorption complex. The reduced symmetry of the adsorbate also leads to a substantial splitting of the stretching and bending modes. In agreement with experiment we show that the main vibrational feature which differentiates coordinatively bonded ammonia from a hydrogen-bonded ammonium ion is the absence of bending modes above 1630 cm(-1) and in the region between 1260 and 1600 cm(-1), and a low-frequency bending band in the range from 1130 to 1260 cm(-1). The calculated distribution of vibrational frequencies agrees very well with the measured infrared adsorption spectra. From the comparison of the adsorption data and the vibrational spectra we conclude that due to the complex adsorption geometry the redshift of the asymmetric stretching is a better measure of the acidity of an active sites than the adsorption energy.

Journal Article↗
PubMed2004

Density-functional study of the cycloaddition of acrylonitrile on the Si(100) surface.

Using a density functional approach, we have explored the cycloaddition of acrylonitrile on the Si(100) surface. The buckling of the surface dimers characteristic for the (2x1) reconstructed surface is shown to favor structures with a dipolar moment such as the resonant form of acrylonitrile with cumulative double bonds. The bond of acrylonitrile via a single C atom is a possible intermediate leading to the nitrile structure of the adsorbed molecule.

Journal Article↗
PubMed2004

Polysaccharides from Hibiscus sabdariffa flowers stimulate proliferation and differentiation of human keratinocytes.

Raw polysaccharides, previously described in detail, were isolated from the flowers of Hibiscus sabdariffa L. and fractionated by ion exchange chromatography into one neutral and three acidic subfractions. Raw polysaccharides and all acidic subfractions caused a strong induction of proliferation of human keratinocytes (HaCaT) of up to 40 %, while the neutral polymers were ineffective. While mitochondrial activity was not influenced, raw polysaccharides induced early differentiation of primary natural human keratinocytes, as determined by involucrin formation.

Cell Division↗
PubMed2004

Baseline staging in cutaneous malignant melanoma.

BACKGROUND: Baseline staging in patients with primary cutaneous malignant melanoma (MM) is routine, but the diagnostic accuracy and the impact on clinical outcome are still unclear. OBJECTIVES: To evaluate the sensitivity and specificity of baseline staging in the early detection of regional lymph node metastases or distant metastases in patients with MM. METHODS: One hundred consecutive patients with MM of Breslow's tumour thickness over 1.0 mm were enrolled. All patients had an extensive baseline staging including physical examination, ultrasound (US) of the abdomen and regional lymph nodes, chest X-ray, whole-body positron emission tomography (PET) and sentinel lymph node biopsy. The sensitivity and specificity of detection of macroscopic or microscopic metastases in the regional lymph nodes or at distant sites were calculated for each method. RESULTS: Sentinel lymph node biopsy was positive in 26 patients. US detected two of 26 histologically tumour-positive sentinel nodes (sensitivity 8%, specificity 88%) and PET two of 26 (sensitivity 8%; specificity 100%). There were three lymph node metastases with a diameter > 4 mm. All of them were found suspect at physical examination. Two of them were detectable with US, two with PET, and all were identified with either US or PET. Nine patients had suspect findings at distant sites, which were all false positive on further investigation (specificity of the combined staging procedures 91%). At 18 (6-37) months' follow-up, five of 26 (19%) patients with a positive sentinel node and four of 74 (5%) of patients with a negative sentinel node had recurrent or progressive disease. CONCLUSIONS: The combination of physical examination and lymph node US detects the great majority of patients with macroscopic lymph node metastasis (approximately 3% of patients at baseline). Only 10% of patients who have a histologically tumour-positive sentinel node are macroscopically detectable. Altogether, approximately 25% of patients have a positive sentinel node biopsy, among 90% microscopic. The value of whole body staging at baseline remains limited, since distant metastases can hardly ever be detected. The survival benefit of baseline staging and surveillance in patients with cutaneous MM remains to be established by comparative prospective trials.

Abdomen↗
PubMed2004

A randomized controlled clinical trial of topical photodynamic therapy with methyl aminolaevulinate in the treatment of actinic keratoses in transplant recipients.

BACKGROUND: Transplant recipients have an increased propensity to develop multiple actinic keratoses, which demonstrate an increased transformation rate into invasive squamous cell carcinoma. OBJECTIVE: To evaluate the efficacy and tolerability of topical photodynamic therapy with the new highly tumour-selective photosensitizer methyl aminolaevulinate vs. placebo in the treatment of actinic keratoses in transplant recipients. METHODS: Seventeen transplant recipients with a total number of 129 mild to moderate actinic keratoses were enrolled in a prospective, randomized, double-blind, placebo-controlled study. Two lesional areas within a patient were randomized for two consecutive treatments of topical photodynamic therapy 1 week apart using either methyl aminolaevulinate or placebo cream. Sites were illuminated with 75 J cm(-2) of visible light delivered at 80 mW cm(-2) by a noncoherent light source. Complete resolution and reduction in the number or size of actinic keratoses within the lesional area relative to the initial findings were evaluated at weeks 4, 8 and 16 after treatment. RESULTS: The lesional areas treated with methyl aminolaevulinate were clinically cleared in 13 of 17 patients at 16 weeks. A partial response was recorded in a further three. No reduction in the size or number of actinic keratoses was observed in one area treated with methyl aminolaevulinate and in all placebo-treated areas. Adverse events, such as erythema, oedema and crust formation, were mild to moderate, and treatment was well tolerated by all patients. CONCLUSION: Photodynamic therapy using methyl aminolaevulinate is a safe and effective treatment for actinic keratoses in transplant recipients. It may also reduce the risk of transformation of actinic keratoses to invasive, potentially fatal, squamous cell carcinoma.

Adult↗
PubMed2004

The spectrum of mesenchymal skin neoplasms reflected by the new WHO classification.

Mesenchymal tumors are a heterogeneous group of tumors often arising in the skin and soft tissue. The tumors have been reclassified by the WHO in 2002. Benign mesenchymal tumors are about a hundred times more frequent than malignant mesenchymal tumors. Clinically, mesenchymal tumors often present as skin-colored nodes. Overall, elderly persons are more affected than younger individuals. The etiology is often unknown, sometimes there is an association with insults such as radiation, scars, or lymphedematous or venous stasis. Whereas some years ago a wide excision with a margin of 3-5 cm was performed for malignant variants, today micrographic surgery is preferred, as it can avoid mutilating procedures. Early detection and removal is critical since mesenchymal skin tumors often cannot be cured by radiation or chemotherapy.

Humans↗
PubMed2003

Proteus syndrome.

A 34-year-old male patient was referred with a recalcitrant leg ulcer overlying an extensive vascular malformation, which had led several times to septic soft tissue infections. During his infancy he had been diagnosed to have Klippel-Trenaunay syndrome. Clinical examination revealed asymmetric hypertrophy of the lower extremities, an extensive portwine stain on the more severely affected left limb as well as prominent venous varicosities of both legs. Hands and feet showed striking cerebriform palmoplantar hypertrophy, and macrodactily with syndactily of several fingers. All toes had been amputated in early childhood due to extreme overgrowth and currently the patient walked on his forefeet in a prominent pes equinus deformity. Further symptoms consisted in several lipomas at both arms, another portwine stain at the left hemithorax and a single café-au-lait spot at the left scapula. Angio-magnetic resonance imaging scans of both legs showed an extensive venous-lymphatic vascular malformation involving the whole subcutis and infiltrating the muscle. The chronic wound was interpreted as venous stasis ulceration. Local percutaneous sclerotherapy of the dilated veins underneath the ulcer was discussed, but considered to carry a relevant risk of skin necrosis with consecutive progression of the wound. A conventional split-skin graft led to complete wound healing. Since, the patient consequently wears custom-made compression stockings and remained free from recurrences. The syndromatic constellation of palmoplantar overgrowth, multiple lipomas, giant fingers and toes, limb overgrowth, venous-lymphatic malformation and a café-au-lait spot led to the diagnosis of Proteus syndrome. The possible aetiology, clinical manifestations, differential diagnosis and management of this rare disorder are discussed.

Adult↗
PubMed2003

Imiquimod in basal cell carcinoma: how does it work?

Imiquimod is a topical immune response modifier that binds to Toll-like receptor-7 and -8, inducing interferon-alpha. We treated superficial basal cell carcinomas (BCC) with imiquimod 5% cream daily for 5-8 days. The BCC lesions were biopsied before treatment and following imiquimod treatment, when the lesion showed the signs of erosion. We applied histology, immunohistochemistry and gene array technology (Affymetrix) to gain further insight into the mode of action of imiquimod. Our findings demonstrate that imiquimod-induced BCC regression is associated with a strong activity of the innate immune response, mediated by cells of macrophage-monocyte origin and is associated with the induction of apoptosis.

Adjuvants, Immunologic↗
PubMed2003

Treatment of verrucous carcinoma with imiquimod and CO2 laser ablation.

An 82-year-old female patient presented with a large perianal hyperkeratotic tumor extending into the anal canal. Staging did not reveal any metastatic spread. Diagnosis of verrucous carcinoma or Buschke-Löwenstein tumor, respectively, was based on typical clinical and histologic features. Moreover, human papillomavirus 6b DNA sequences could be detected by PCR. Surgical excision could not be performed due to the general health status of the patient; thus, alternative therapy methods were necessary. Treatment with imiquimod cream 5% (Aldara), a topical immune response modifier applied once a day and left for 12 h, led to significant partial tumor regression and clear demarcation of the tumor. The remaining tumor, now feasible for treatment with CO2 laser, was removed in two sessions in local anesthesia. In a third session, tumor parts in the anal canal were vaporized. This case demonstrates that the combination of imiquimod and CO2 laser ablation is an effective treatment option for verrucous carcinoma.

Aged↗
PubMed2002

Shear instability of gamma-Fe in bulk and in ultrathin films.

Using ab initio local-spin-density calculations we demonstrate that along the Bain path describing the transformation of face-centered-cubic (fcc) gamma-Fe into body-centered-cubic (bcc) alpha-Fe, tetragonal Fe is unstable against monoclinic shear deformations producing a nearly bcc structure. In the limit of a monolayer adsorbed on a fcc substrate, the epitaxial constraint suppresses the shear instability, but in ultrathin films with three to six monolayers a striped pattern of near-bcc domains develops, confirming recent observations by scanning tunneling microscopy. A strong correlation between the shear instability and the magnetic state is reported.

Journal Article↗