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1.
Langmuir ; 39(40): 14396-14403, 2023 Oct 10.
Article in English | MEDLINE | ID: mdl-37755138

ABSTRACT

Despite its unrivaled hardness, diamond can be severely worn during the interaction with others, even softer materials. In this work, we calculate from first-principles the energy and forces necessary to induce the atomistic wear of diamond and compare them for different surface orientations and passivation by oxygen, hydrogen, and water fragments. The primary mechanism of wear is identified as the detachment of the carbon chains. This is particularly true for oxidized diamond and diamonds interacting with silica. A very interesting result concerns the role of stress, which reveals that compressive stresses can highly favor wear, making it even energetically favorable.

2.
J Chem Theory Comput ; 19(15): 5231-5241, 2023 Aug 08.
Article in English | MEDLINE | ID: mdl-37402165

ABSTRACT

High-throughput first-principles calculations, based on solving the quantum mechanical many-body problem for hundreds of materials in parallel, have been successfully applied to advance many materials-based technologies, from batteries to hydrogen storage. However, this approach has not yet been adopted to systematically study solid-solid interfaces and their tribological properties. To this aim, we developed TribChem, an advanced software program based on the FireWorks platform, which is here presented and released. TribChem is constructed in a modular way, allowing for the separate calculation of bulk, surface, and interface properties. At present, the calculated interfacial properties include adhesion, shear strength, and charge redistribution. Further properties can be easily added due to the general structure of the main workflow. TribChem contains a high-level interface class to store/retrieve results from its own database and connect to public databases.

3.
ACS Appl Mater Interfaces ; 15(15): 19624-19633, 2023 Apr 19.
Article in English | MEDLINE | ID: mdl-37015021

ABSTRACT

Adhesion energy, a measure of the strength by which two surfaces bind together, ultimately dictates the mechanical behavior and failure of interfaces. As natural and artificial solid interfaces are ubiquitous, adhesion energy represents a key quantity in a variety of fields ranging from geology to nanotechnology. Because of intrinsic difficulties in the simulation of systems where two different lattices are matched, and despite their importance, no systematic, accurate first-principles determination of heterostructure adhesion energy is available. We have developed robust, automatic high-throughput workflow able to fill this gap by systematically searching for the optimal interface geometry and accurately determining adhesion energies. We apply it here for the first time to perform the screening of around a hundred metallic heterostructures relevant for technological applications. This allows us to populate a database of accurate values, which can be used as input parameters for macroscopic models. Moreover, it allows us to benchmark commonly used, empirical relations that link adhesion energies to the surface energies of its constituent and to improve their predictivity employing only quantities that are easily measurable or computable.

4.
Nanoscale Adv ; 4(19): 4175-4184, 2022 Sep 27.
Article in English | MEDLINE | ID: mdl-36285223

ABSTRACT

Friction force microscopy measurements reveal a dramatic difference of a factor 3 between the friction forces experienced on single-monolayer graphene on top of oxidized and unoxidized copper substrates. We associate this difference with the strong and weak adhesion that the graphene experiences on these two substrates, respectively, but argue that it is too large to be ascribed either to a difference in contact area or to a difference in contact commensurability or even to a combination of these two effects. We use density functional theory to show a significant increase in the chemical reactivity of graphene when it is curved.

5.
J Phys Chem A ; 124(39): 8005-8010, 2020 Oct 01.
Article in English | MEDLINE | ID: mdl-32881495

ABSTRACT

Among metal ß-diketonates, nickel acetylacetonate (Ni(acac)2) has been widely employed as a precursor for many chemical structures, due to its catalytic properties. Here, we investigate, by means of density functional theory (DFT) calculations, the adsorption and dissociation of this complex: after an evaluation of the structural and electronic properties of Ni(acac)2, a comparison between different dissociation patterns reveals that the most favorable pattern for the complex adsorbed on iron is different from the one suggested by considering the strength of the bonds in the isolated complex and an attempt to generalize this dissociation model is made in this work. Moreover, the most favorable adsorption configurations turned out to be a long bridge positioning of the nickel atom along with an on top positioning of the oxygen atoms of Ni(acac)2, while a short bridge positioning is the most favorable for the central metallic unit alone.

6.
Sci Rep ; 9(1): 17062, 2019 Nov 19.
Article in English | MEDLINE | ID: mdl-31745097

ABSTRACT

We present a comprehensive ab initio, high-throughput study of the frictional and cleavage strengths of interfaces of elemental crystals with different orientations. It is based on the detailed analysis of the adhesion energy as a function of lateral, γ(x, y), and perpendicular displacements, γ(z), with respect to the considered interface plane. We use the large amount of computed data to derive fundamental insight into the relation of the ideal strength of an interface plane with its adhesion. Moreover, the ratio between the frictional and cleavage strengths is provided as good indicator for the material failure mode - dislocation propagation versus crack nucleation. All raw and curated data are made available to be used as input parameters for continuum mechanic models, benchmarks, or further analysis.

7.
J Phys Chem A ; 123(32): 7007-7015, 2019 Aug 15.
Article in English | MEDLINE | ID: mdl-31318554

ABSTRACT

Molybdenum dithiocarbamate (MoDTC) is a well-known lubricant additive, which, in tribological conditions, is capable of forming layers of MoS2 with excellent friction reduction properties. Despite being widely employed in commercial engine oils, a comprehensive theoretical description of the properties of MoDTC is still lacking. In this work, we employ density functional theory to study the structural, electronic, and vibrational properties of MoDTC. We investigate the relative stability of different isomers, different hydrocarbon terminations, and oxidized complexes. Oxidation was found to be energetically favorable for a wide range of conditions, and the most favorable position for oxygen atoms in MoDTC turned out to be the ligand position. These results, along with the calculated reaction energies for different dissociation paths, can be useful to better identify the elementary steps of the decomposition process of MoDTC.

8.
Phys Rev Lett ; 121(2): 026804, 2018 Jul 13.
Article in English | MEDLINE | ID: mdl-30085711

ABSTRACT

We derive a connection between the intrinsic tribological properties and the electronic properties of a solid interface. In particular, we show that the adhesion and frictional forces are dictated by the electronic charge redistribution occurring due to the relative displacements of the two surfaces in contact. We define a figure of merit to quantify such a charge redistribution and show that simple functional relations hold for a wide series of interactions including metallic, covalent, and physical bonds. This suggests unconventional ways of measuring friction by recording the evolution of the interfacial electronic charge during sliding. Finally, we explain that the key mechanism to reduce adhesive friction is to inhibit the charge flow at the interface and provide examples of this mechanism in common lubricant additives.

9.
J Neural Eng ; 14(4): 046003, 2017 08.
Article in English | MEDLINE | ID: mdl-28382924

ABSTRACT

OBJECTIVE: As artificial prostheses become more refined, they are most often used as a therapeutic option for hand amputation. By contrast to extra- or intraneural interfaces, regenerative nerve electrodes are designed to enable electrical interfaces with regrowing axonal bundles of injured nerves, aiming to achieve high selectivity for recording and stimulation. However, most of the developed designs pose an obstacle to the regrowth mechanisms due to low transparency and cause impairment to the nerve regeneration. APPROACH: Here we present the double-aisle electrode, a new type of highly transparent, non-obstructive regenerative electrode. Using a double-side thin-film polyimide planar multi-contact electrode, two nerve fascicles can regenerate without physical impairment through two electrically isolated aisles. MAIN RESULTS: We show that this electrode can be used to selectively record and stimulate fascicles, acutely as well as chronically, and allow regeneration in nerve gaps of several millimeters without impairment. SIGNIFICANCE: This multi-aisle regenerative electrode may be suitable for neuroprosthetic applications, such as prostheses, for the restoration of hand function after amputation or severe nerve injuries.


Subject(s)
Electrodes, Implanted , Miniaturization/methods , Nerve Regeneration/physiology , Peripheral Nerves/physiology , Action Potentials/physiology , Animals , Electric Stimulation/methods , Female , Microelectrodes , Rats , Rats, Sprague-Dawley
10.
Phys Rev Lett ; 111(14): 146101, 2013 Oct 04.
Article in English | MEDLINE | ID: mdl-24138257

ABSTRACT

Tribochemical reactions are chemical processes, usually involving lubricant or environment molecules, activated at the interface between two solids in relative motion. They are difficult to be monitored in situ, which leaves a gap in the atomistic understanding required for their control. Here we report the real-time atomistic description of the tribochemical reactions occurring at the interface between two diamond films in relative motion, by means of large scale ab initio molecular dynamics. We show that the load-induced confinement is able to catalyze diamond passivation by water dissociative adsorption. Such passivation decreases the energy of the contacting surfaces and increases their electronic repulsion. At sufficiently high coverages, the latter prevents surface sealing, thus lowering friction. Our findings elucidate effects of the nanoscale confinement on reaction kinetics and surface thermodynamics, which are important for the design of new lubricants.

11.
Langmuir ; 27(11): 6862-7, 2011 Jun 07.
Article in English | MEDLINE | ID: mdl-21545120

ABSTRACT

We propose a method to calculate the ideal shear strength τ of two surfaces in contact by ab initio calculations. This quantity and the work of adhesion γ are the interfacial parameters usually derived from tip-based friction force measurements. We consider diamond interfaces and quantitatively evaluate the effects of surface orientation and passivation. We find that in the case of fully passivated interfaces, γ is not affected by the orientation and the alignment of the surfaces in contact. On the contrary, τ does show a dependence on the atomic-scale roughness of the interface. The surface termination has a major impact on the tribological properties of diamond. The presence of dangling bonds, even at concentrations low enough to prevent the formation of interfacial C-C bonds, causes an increase in the resistance to sliding by 2 orders of magnitude with respect to the fully hydrogenated case. We discuss our findings in relation to experimental observations.

12.
Drug Dev Ind Pharm ; 35(1): 73-82, 2009 Jan.
Article in English | MEDLINE | ID: mdl-18821153

ABSTRACT

Commercial tablets of glyburide exhibit unsatisfactory dissolution profiles and, consequently, problems of bioinequivalence and poor bioavailability. The aim of this work was to develop glyburide fast-dissolving tablets by exploiting the solubilizing effect of different cyclodextrins (CDs), alone or in combination with hydrophilic polymers. Drug-CD and drug-CD-polymer systems, prepared by different techniques, were characterized by differential scanning calorimetry (DSC), X-ray diffractometry, and Fourier transform infra-red (FT-IR) spectroscopy. Tablets containing binary and ternary systems were prepared by direct compression and evaluated for technological properties and dissolution behavior in comparison with a reference formulation containing the plain drug. A significant improvement of the drug dissolution profile was achieved from tablets containing drug-CD systems (coevaporated products doubled drug dissolution efficiency [DE]), but 100% drug dissolution was never reached. Better results were obtained with ternary systems. In particular, polyvinylpyrrolidone (PVP) emerged as the most effective polymer, and tablets with drug-PVP-hydroxypropyl-betaCD coevaporated products showed the best dissolution profiles, reaching 100% dissolved drug within only 15 min.


Subject(s)
Cyclodextrins/chemistry , Glyburide/pharmacokinetics , Hypoglycemic Agents/pharmacokinetics , Polymers/chemistry , Biological Availability , Calorimetry, Differential Scanning , Chemistry, Pharmaceutical , Glyburide/chemistry , Hypoglycemic Agents/chemistry , Povidone/chemistry , Solubility , Spectroscopy, Fourier Transform Infrared , Tablets , Technology, Pharmaceutical , Therapeutic Equivalency , X-Ray Diffraction
13.
Phys Rev Lett ; 99(17): 176101, 2007 Oct 26.
Article in English | MEDLINE | ID: mdl-17995348

ABSTRACT

In this Letter we show that friction of anticorrugating systems can be dramatically decreased by applying an external load. The counterintuitive behavior that deviates from the macroscopic Amonton law is dictated by quantum mechanical effects that induce a transformation from anticorrugation to corrugation in the near-surface region. We describe the load-driven modifications occurring in the potential energy surface of different rare gas-metal adsorbate systems, namely, Ar, Kr, Xe on Cu(111), and Xe on Ag(111), and we calculate the consequent friction drop for the commensurate Xe/Cu system by means of combined ab initio and classical molecular dynamics simulations.

14.
Article in English | MEDLINE | ID: mdl-18002961

ABSTRACT

This paper describes a data-driven Decision Support System for Electroencephalography (EEG) signals acquisition, and parallel elaboration based on the integration of an Ambient Intelligent (AmI) [1] platform and a GRID enabled Infrastructure. The paper explores the analysis and design of the environment, the real-time data acquisition, the integration of the acquired data in dedicated EHR, and the EEG processing through parallel analysis algorithm available on the GRID infrastructure. After an overview of background concepts, the paper presents a brief description of the environment architecture, and a detailed analysis of the EEG algorithm. The challenge of the work presented is to effectively show how medical data can be shared and processed by exploiting the resources and capabilities of both the AmI platform and the GRID infrastructure. This particular Decision Support System, shows how it is possible to improve patient safety, quality of care, and efficiency in healthcare delivery.


Subject(s)
Algorithms , Decision Making, Computer-Assisted , Electroencephalography/instrumentation , Electroencephalography/methods , Signal Processing, Computer-Assisted/instrumentation , Humans
15.
Phys Rev Lett ; 91(13): 136101, 2003 Sep 26.
Article in English | MEDLINE | ID: mdl-14525319

ABSTRACT

We present first-principle calculations on the initial stages of SiC homoepitaxial growth on the beta-SiC(111)-(sqrt[3]xsqrt[3]) surface. We show that the nonstoichiometric reconstruction plays a relevant role in favoring the attainment of high-quality films. The motivation is twofold: On one hand, we find that the reconstruction controls the kinetics of adatom incorporation; on the other hand, we observe that the energy gain upon surface stability can induce the reorganization of the deposited material into a crystalline structure, thus revealing that a surface-driven mechanism is able to stabilize defect-free layer deposition on Si-rich surfaces.

16.
Haematologica ; 88(5): ECR18, 2003 May.
Article in English | MEDLINE | ID: mdl-12745287

ABSTRACT

Based on its ability to inhibit the tyrosine kinase activity of ABL, as well as the c-kit and the Platelet Derived Growth Factor Receptor tyrosine kinases, the spectrum of diseases that may respond to STI571 is increasing. A recently recognized subgroup of myeloproliferative disorders/myelodysplastic syndromes (MPD/MDS) has a t(5;12)(q33;p13) with the activation of the gene for PDGFBR which encodes a receptor tyrosine kinase. Here, we present the case of a patient, with MPD/MDS, and eosinophilia, carrying a translocation t(5;12)(q33;p13) who achieved a complete remission following treatment with STI571, 400 mg daily. At the time of writing he still remains in complete remission with an excellent performance status. There is clearly a need for further studies of STI 571in MPD/MDS with chromosomal translocations involving PDGFBR to confirm this promising initial result.


Subject(s)
Antineoplastic Agents/therapeutic use , Enzyme Inhibitors/therapeutic use , Leukemia, Myelomonocytic, Chronic/drug therapy , Piperazines/therapeutic use , Pyrimidines/therapeutic use , Receptor, Platelet-Derived Growth Factor beta/genetics , Aged , Benzamides , Eosinophilia/diagnosis , Eosinophilia/drug therapy , Humans , Imatinib Mesylate , Leukemia, Myelomonocytic, Chronic/diagnosis , Male , Myelodysplastic Syndromes/diagnosis , Myelodysplastic Syndromes/drug therapy , Myeloproliferative Disorders/diagnosis , Myeloproliferative Disorders/drug therapy , Receptor, Platelet-Derived Growth Factor beta/antagonists & inhibitors , Translocation, Genetic
17.
Pathology ; 34(5): 423-6, 2002 Oct.
Article in English | MEDLINE | ID: mdl-12408340

ABSTRACT

AIMS: Hep Par 1 has been described as a specific marker of hepatocellular differentiation and its immunohistochemical use has been suggested as a helpful tool for hepatocellular carcinoma (HCC) diagnosis. Most metastatic liver tumours come from the gastrointestinal tract and usually can be distinguished from HCC only through histology. We evaluated by immunohistochemistry the specificity of Hep Par 1, studying the presence of the epitope that reacts with Hep Par 1 in primary gastric and colorectal cancers. METHODS: A series of 39 cases of primary gastric and 18 cases of colorectal carcinoma were selected. Twenty-six of the 39 gastric carcinomas were of the intestinal type, six of the diffuse type, three of the mixed type and five had hepatoid differentiation. Two of the 18 colorectal adenocarcinomas were well differentiated, 14 moderately differentiated, one poorly differentiated and one was of the mucinous type. Five-microm sections were stained by immunohistochemistry using Hep Par 1 as primary antibody. RESULTS: Immunohistochemical staining was observed in 26 gastric carcinomas (69%) and nine large bowel carcinomas (50%). Fifteen of the 26 positive-stained gastric cancers were of intestinal type, four of diffuse type and two of mixed type cases. All of the five hepatoid type cases stained positively. Two of the nine positively stained colorectal cancers were well differentiated, six were moderately differentiated and one was a mucinous type adenocarcinoma. The staining pattern was cytoplasmic and granular as described in benign and malignant hepatocytes. The percentage of immunostained cells was graded as follows: 0 (no staining); 1 (>0-5%); 2 (> 5-50%); 3 (> 50%). Of the 26 positive gastric tumours, 13 showed a staining score of 1, eight scored 2, and five scored 3. Four of the nine positive intestinal carcinomas showed a staining score of 1, and five scored 2. CONCLUSIONS: Our results show that Hep Par 1 is a highly sensitive marker of hepatocellular differentiation as demonstrated by the expression in gastric tumours with hepatoid histotype. However, the frequent reaction with neoplastic cells of gastric and bowel carcinomas shows a low grade of specificity of this antibody.


Subject(s)
Adenocarcinoma/chemistry , Biomarkers, Tumor/analysis , Colorectal Neoplasms/chemistry , Stomach Neoplasms/chemistry , Adenocarcinoma/classification , Adenocarcinoma/immunology , Antibodies, Monoclonal/immunology , Antigens, Neoplasm/analysis , Antigens, Neoplasm/immunology , Biomarkers, Tumor/immunology , Colorectal Neoplasms/classification , Colorectal Neoplasms/immunology , Epitopes , Humans , Immunoenzyme Techniques , Sensitivity and Specificity , Stomach Neoplasms/classification , Stomach Neoplasms/immunology
20.
Phys Rev Lett ; 87(7): 076802, 2001 Aug 13.
Article in English | MEDLINE | ID: mdl-11497907

ABSTRACT

First-principles calculations are used to investigate the electronic properties of the surfaces of polyethylene. The calculations support the experimental evidence of a negative electron affinity, with calculated values of -0.17 eV and -0.10 eV for surfaces with chains perpendicular and parallel to the surface normal, respectively. Both surfaces exhibit a surface state with binding energy -1.2 +/- 0.5 eV with respect to the bulk polyethylene conduction band minimum. Implications of these findings on spectroscopy, as well as on the transport and aging properties of polyethylene for high-voltage applications, are discussed.

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