Low thermal conductivity of peanut-shaped carbon nanotube and its insensitive response to uniaxial strain.

Motivated by the experimental synthesis of peanut-shaped carbon nanotubes (PSNTs) that combine the novel features of fullerene and carbon nanotubes (CNTs), we study the thermal conductivity of a PSNT (1dp08) and its response to different strains by using non-equilibrium molecular dynamics simulations and lattice dynamics together with density functional theory. We find that the thermal conductivity of the PSNT is reduced by more than 90% as compared to that of CNTs, and remains almost the same when different strains applied, exhibiting very different behaviors from that of CNTs, where the thermal conductivity decreases monotonically with the increase of strain. Through phonon mode calculations, we show that the reduced phonon group velocity, phonon lifetime and the vibrational mismatch are responsible for the low thermal conductivity of the PSNT, and the insensitive response of thermal conductivity to strain is due to the insensitivity of its phonon density of states and group velocity to strain. These features endow the PSNT with the potential applications in thermal devices, and add new features to one-dimensional carbon nanomaterials going beyond conventional CNTs.

Can interaction with informal urban green space reduce depression levels? An analysis of potted street gardens in Tangier, Morocco.

OBJECTIVES: The purpose of this study was to investigate the association between ownership of a potted street garden (PSG) and depression levels in a densely populated, disadvantaged Moroccan neighbourhood. STUDY DESIGN: The study design used was a cross-sectional study. METHODS: Data were collected through a face-to-face survey conducted in January 2019. In total, there were 388 participants, in three densely populated neighbourhoods of the Beni-Makada district of Tangier, Morocco. We measured depression levels using the Patient Health Questionnaire-9 and data were analysed using weighted moderated ordinary least squared regression analysis. RESULTS: PSG ownership was associated with a .74-point increase in depression score (b = .74, 95% confidence interval [CI] = .38, 1.10, ß = .22, Variance Inflation Factor (VIF) = 1.15; P < .001). PSG ownership also moderated the negative association between depression levels and neighbourhood life satisfaction (F [3,336] = 5.058, P < .001, R2 change = .039). A one-level increase in PSG being perceived as a public amenity by their owners was associated with a .36-point decrease in depression score (b = -.36, 95% CI = -.71, -.01, ß = -.14, VIF = 1.08; P < .05), whereas a 1-min increase in PSG daily care duration was associated with .04-point increase in depression score (b = .04, 95% CI = .01, .06, ß = .24, VIF = 1.68; P < .01). CONCLUSIONS: Our findings suggest that PSG ownership might have a negative impact on mental health in densely populated, disadvantaged neighbourhoods. This negative association might be due to the fact of PSGs being deemed as private property present in an unsafe and uncontrolled environment.

Insight into the vertical detachment energy oscillation of Na(n)C60(-) clusters.

We have performed a detailed density functional theory study on the structural and electronic properties of Na(n)C(60)(-) (n = 1-12) clusters. The calculated vertical detachment energies show good agreement with the experimental data, which confirms the 3p (n = 3p) oscillation rule. The oscillation can be attributed to the combination of the charge depletion distribution induced by removing electrons and the number of the sodium atoms in direct contact with the fullerene. Based on the structural and electronic properties, the Na atoms can be categorized into two groups, one is for the metal atoms directly bonded to the fullerene surface, and the other one is for those without bonding to the fullerene. The Na atoms in group one would donate electrons to both the fullerene and the Na atoms in group two. As the total number of the sodium atoms increases, the number of Na atoms in group one would continue increasing till the size n = 3p - 1 to meet a shoulder from n = 3p - 1 to n = 3p, which accounts for the maximum vertical detachment energy at the size of n = 3p as drawn from the detailed electronic property studies.

Coinage metal (4, 4) nanotubes, simulated by first-principles calculations.

The structural stability of coinage metal nanotubes with a square cross-section has been investigated by the first-principles numerical simulations. In addition to the reported (4, 4) silver tube, it is found that the hollow (4, 4) copper and gold nanotubes can also be formed by applying an appropriate stress to an 8(A)/8(B) fcc wire. The stability of these coinage metal (4, 4) nanotubes, formed by tip-stretching the wires, has been explained by a local minimum in the string tension variation with their tube lengths. Interestingly, we have explained why a low-stress stretching is needed to obtain the (4, 4) Cu tube in contrast to a higher one for both the (4, 4) Ag and Au tubes due to the larger stiffness coefficient of copper than those of silver and gold, which could be proved by future experiments.

Gate-controlled current and inelastic electron tunneling spectrum of benzene: a self-consistent study.

We use density functional theory based nonequilibrium Green's function to self-consistently study the current through the 1,4-benzenedithiol (BDT). The elastic and inelastic tunneling properties through this Au-BDT-Au molecular junction are simulated, respectively. For the elastic tunneling case, it is found that the current through the tilted molecule can be modulated effectively by the external gate field, which is perpendicular to the phenyl ring. The gate voltage amplification comes from the modulation of the interaction between the electrodes and the molecules in the junctions. For the inelastic case, the electron tunneling scattered by the molecular vibrational modes is considered within the self-consistent Born approximation scheme, and the inelastic electron tunneling spectrum is calculated.

Signal transducer and activator of transcription (STAT)-induced STAT inhibitor 1 (SSI-1)/suppressor of cytokine signaling 1 (SOCS1) inhibits insulin signal transduction pathway through modulating insulin receptor substrate 1 (IRS-1) phosphorylation.

Signal transducer and activator of transcription (STAT)-induced STAT inhibitor 1 (SSI-1) is known to function as a negative feedback regulator of cytokine signaling, but it is unclear whether it is involved in other biological events. Here, we show that SSI-1 participates and plays an important role in the insulin signal transduction pathway. SSI-1-deficient mice showed a significantly low level of blood sugar. While the forced expression of SSI-1 reduced the phosphorylation level of insulin receptor substrate 1 (IRS-1), SSI-1 deficiency resulted in sustained phosphorylation of IRS-1 in response to insulin.Furthermore, SSI-1 achieves this inhibition both by binding directly to IRS-1 and by suppressing Janus kinases. These findings suggest that SSI-1 acts as a negative feedback factor also in the insulin signal transduction pathway through the suppression of IRS-1 phosphorylation.

Tuning magnetic properties of Mn(4) cluster with gold coating.

The magnetic properties of transition metal clusters are a unique function of their size and differ from their bulk behavior due to quantum confinement. Here we show that surface modification provides another channel to tune their magnetic properties. This is demonstrated by taking Mn(4) as an example. Although Mn(4) carries a giant magnetic moment of 20 micro(B), the magnetic coupling can be tuned from ferromagnetic to ferrimagnetic by changing the number of gold atoms coated on its surface. We found that 26 gold atoms are needed to fully cover a Mn(4) cluster. When partially coated, the system exhibits ferromagnetic coupling with a total magnetic moment of 18 micro(B) and it becomes ferrimagnetic with a moment of 8 micro(B) when fully coated. This magnetic cross-over is caused by the shrinking of the Mn-Mn bond length, suggesting that the magnetic properties of a Mn(4) cluster can be tuned by controlling the surface coverage.

Ferromagnetism in semihydrogenated graphene sheet.

Single layer of graphite (graphene) was predicted and later experimentally confirmed to undergo metal-semiconductor transition when fully hydrogenated (graphane). Using density functional theory we show that when half of the hydrogen in this graphane sheet is removed, the resulting semihydrogenated graphene (which we refer to as graphone) becomes a ferromagnetic semiconductor with a small indirect gap. Half-hydrogenation breaks the delocalized pi bonding network of graphene, leaving the electrons in the unhydrogenated carbon atoms localized and unpaired. The magnetic moments at these sites couple ferromagnetically with an estimated Curie temperature between 278 and 417 K, giving rise to an infinite magnetic sheet with structural integrity and magnetic homogeneity. This is very different from the widely studied finite graphene nanostrucures such as one-dimensional nanoribbons and two-dimensional nanoholes, where zigzag edges are necessary for magnetism. From graphene to graphane and to graphone, the system evolves from metallic to semiconducting and from nonmagnetic to magnetic. Hydrogenation provides a novel way to tune the properties with unprecedented potentials for applications.

Non-regular hexagonal 2D carbon, an allotrope of graphene: a first-principles computational study.

In a first principle computational study, using density functional theory, we have identified four types of 2D carbon sheets, similar to graphene, made entirely of non-regular hexagons. In one case, we get a structure where the non-regular hexagons have four sides of length d1 = 1.416 Å and two sides of length d2 = 1.68 Å. Next case, in the non-regular hexagons the side d1 (two times) and d2 (four times) are exchanged. In two other cases, the non-regular hexagons have three pairs (opposite sides) of different lengths (d1 = 1.529 Å, d2 = 1.567 Å, and d3 = 1.612 Å; d1 = 1.387 Å, d2 = 1.348 Å, and d3 = 1.387 Å). By propper choice of the non-regular hexagon sides, one could arrive at a 2D carbon system like graphene, but with a tunable band gap. The structure is more stable when the system has more number of regular C-C bonds than the longer C-C bonds. Due to its non-regular hexagons, special atomic configuration, this system may have, like graphene, unusual properties. It is semiconducting, and there is no need to functionalize it for opening the band gap as is the case with graphene.

Penta-BCN: A New Ternary Pentagonal Monolayer with Intrinsic Piezoelectricity.

Going beyond conventional hexagonal sheets, pentagonal 2D structures are of current interest due to their novel properties and broad applications. Herein, for the first time, we study a ternary pentagonal BCN monolayer, penta-BCN, which exhibits intrinsic piezoelectric properties. Based on state-of-the-art theoretical calculations, we find that penta-BCN is stable mechanically, thermally, and dynamically and has a direct band gap of 2.81 eV. Due to its unique atomic configuration with noncentrosymmetric and semiconducting features, penta-BCN displays high spontaneous polarization of 3.17 × 10-10 C/m and a prominent piezoelectricity with d21 = 0.878 pm/V, d22 = -0.678 pm/V, and d16 = 1.72 pm/V, which are larger than those of an h-BN sheet and functionalized pentagraphene. Since B, C, and N are rich in resources, light in mass, and benign to the environment, the intrinsic polarization and piezoelectricity make the penta-BCN monolayer promising for technological applications. This study expands the family of 2D pentagonal structures with new features.

Stabilization of square planar silicon: a new building block for conjugated Si-containing systems.

The feasibility of square planar silicon as a building block for conjugated systems was investigated by ab initio calculations. A five-membered ring model system was used to map electronic and steric substituent effects that might help in the stabilization of the planar structure. A pi push-pull arrangement around the silicon was found to prefer planarity. Aromaticity was proven to play an important role in stabilization as well. With the help of steric constraints, a new structure was proposed as a synthetic target containing square planar silicon. The kinetic stability of this structure was also investigated.

Polarization-induced switching effect in graphene nanoribbon edge-defect junction.

With nonequilibrium Green's function approach combined with density functional theory, we perform an ab initio calculation to investigate transport properties of graphene nanoribbon (GNR) junctions self-consistently. Tight-binding approximation is applied to model the zigzag (ZGNR) electrodes, and its validity is confirmed in comparison to the GAUSSIAN03 periodic boundary condition calculation result of the same system. The origin of abnormal jump points usually appearing in the transmission spectrum is explained with the detailed tight-binding ZGNR band structure. Transport property of an edge-defect ZGNR junction is investigated, and the tunable tunneling current can be sensitively controlled by transverse electric fields.

A theoretical exploration of the intermolecular interactions between resveratrol and water: a DFT and AIM analysis.

The polyphenolic compound resveratrol, classified under stilbenes, offers a broad range of health advantages, including neuroprotection and playing a role in autophagy in the nervous system. However, resveratrol has poor water solubility and is soluble in the gel phase in liposomal membranes. The main aim of this work was to understand the nature of the interactions between resveratrol and water molecules. In the present study, we used the dispersion corrected density functional theory (DFT) method to study hydrogen bonding interactions. Eight different geometries of resveratrol-water complexes were identified by optimizing the geometries by placing water at various locations. We observed the two lowest energy structures to be isoenergetic. In most complexes, water interaction occurs with phenolic hydrogen as all the phenolic hydroxyl groups have identical Vs,max values. Energy decomposition analysis shows that the dispersion contribution was minimal in these complexes, while electrostatic and orbital contributions were larger. Complex formation between water and the resveratrol molecule results in a blue shift in the vibrational frequency, along with an increase in intensity due to the transfer of electron density. The hydrogen bonds in the resveratrol-water complexes have closed-shell interactions with a medium-to-strong bonding nature. Noncovalent index analysis of the complexes shows that, in addition to hydrogen bonding, electrostatic and van der Waal's interactions play a key role in stabilizing the complexes. Graphical abstract Noncovalent index analysis showing that, in addition to hydrogen bonding, electrostatic and van der Waal's interactions play a major role in stabilizing resveratrol-water complexes.

Interaction of gas molecules with Ti-benzene complexes.

Using first-principles calculations based on gradient corrected density functional theory, we have studied the interaction of NH(3), H(2), and O(2) with Ti-benzene complexes [Ti(Bz)(2) and Ti(2)(Bz)(2)]. The energy barriers as the gas molecules approach the Ti-benzene complexes as well as the geometries of the ground state of these interacting complexes were obtained by starting with several initial configurations. While NH(3) and H(2) were found to physisorb on the Ti(Bz)(2) complex, the O(2) reacts with it strongly leading to dissociative chemisorption of the oxygen molecule. In contrast all the gas molecules react with the Ti(2)(Bz)(2) complex. These studies indicate that the reaction of certain, but not all, gas molecules can be used to probe the equilibrium geometries of organometallic complexes. Under special conditions, such as high pressure, the Ti atom intercalated between benzene molecules in Ti(Bz)(2) and the Ti(2)(Bz)(2) complexes could store hydrogen in chemisorbed states. The results are compared to available experimental data.

Current through single conjugated molecules: calculations versus measurements.

We use density functional theory based nonequilibrium Green's function to calculate the current through the different rodlike molecules at the finite temperatures self-consistently, which was compared to the experimental measurements presented by Reichert et al. [Phys. Rev. Lett. 88, 176804 (2002)] and by Mayor et al. [Angew. Chem. Int. Ed. 42, 5834 (2003)], respectively. Our results agree with the measurements very well, especially for the bias around +/-1.0 V. The investigation of the topological effect for the symmetrical molecule reveals the fact that the para position compound provides a considerably larger conductance than the meta one.

Crystal-like low frequency phonons in the low-density amorphous and high-density amorphous ices.

The structure and vibrational properties of high- and low-density amorphous (HDA and LDA, respectively) ices have been determined using reverse Monte Carlo, molecular dynamics, and lattice dynamics simulations. This combined approach leads to a more accurate and detailed structural description of HDA and LDA ices when compared to experiment than was previously possible. The water molecules in these ices form well connected hydrogen-bond networks that exhibit modes of vibration that extend throughout the solid and can involve up to 70% of all molecules. However, the networks display significant differences in their dynamical behavior. In HDA, the extended low-frequency vibrational modes occur in dense parallel two dimensional layers of water that are approximately 10 nm thick. In contrast, the extended modes in LDA resemble a holey structure that encapsulates many small pockets of nonparticipating water molecules.

An ontology-based mediator of clinical information for decision support systems: a prototype of a clinical alert system for prescription.

OBJECTIVE: We have been developing a decision support system that uses electronic clinical data and provides alerts to clinicians. However, the inference rules for such a system are difficult to write in terms of representing domain concepts and temporal reasoning. To address this problem, we have developed an ontology-based mediator of clinical information for the decision support system. METHODS: Our approach consists of three steps: 1) development of an ontology-based mediator that represents domain concepts and temporal information; 2) mapping of clinical data to corresponding concepts in the mediator; 3) temporal abstraction that creates high-level, interval-based concepts from time-stamped clinical data. As a result, we can write a concept-based rule expression that is available for use in domain concepts and interval-based temporal information. The proposed approach was applied to a prototype of clinical alert system, and the rules for adverse drug events were executed on data gathered over a 3-month period. RESULTS: The system generated 615 alerts. 346 cases (56%) were considered appropriate and 269 cases (44%) were inappropriate. Of the false alerts, 192 cases were due to data inaccuracy and 77 cases were due to insufficiency of the temporal abstraction. CONCLUSION: Our approach enabled to represent a concept-based rule expression that was available for the prototype of a clinical alert system. We believe our approach will contribute to narrow the gaps of information model between domain concepts and clinical data repositories.

Extensive first-principles molecular dynamics study on Li encapsulation into C60 and its experimental confirmation.

The aim of increasing the production ratio of endohedral C60 by impinging foreign atoms against C60 is a crucial matter of the science and technology employed towards industrialization of these functional building block materials. Among these endohedral fullerenes, Li+@C60 exhibits a wide variety of physical and chemical phenomena and has the potential to be applicable in areas spanning the medical field to photovoltaics. However, currently, Li+@C60 can be experimentally produced with only ∼1% ratio using the plasma shower method with a 30 eV kinetic energy provided to the impinging Li+ ion. From extensive first-principles molecular dynamics simulations, it is found that the maximum production ratio of Li+@C60 per hit is increased to about 5.1% (5.3%) when a Li+ ion impinges vertically on a six-membered ring of C60 with 30 eV (40 eV) kinetic energy, although many C60 molecules are damaged during this collision. On the contrary, when it impinges vertically on a six-membered ring with 10 eV kinetic energy, the production ratio remains at 1.3%, but the C60 molecules are not damaged at all. On the other hand, when the C60 is randomly oriented, the production ratio reduces to about 3.7 ± 0.5%, 3.3 ± 0.5%, and 0.2 ± 0.03% for 30 eV, 40 eV, and 10 eV kinetic energy, respectively. Based on these observations we demonstrate the possibility of increasing the production ratio by fixing six-membered rings atop C60 using the Cu(111) substrate or UV light irradiation. In order to assess the ideal experimental production ratio, the 7Li solid NMR spectroscopy measurement is also performed for the multilayer randomly oriented C60 sample irradiated by Li+ using the plasma shower method combined with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Time-of-flight mass spectroscopy measurements are also performed to cross check whether Li+@C60 molecules are produced in the sample. The resulting experimental estimate, 4% for 30 eV incident kinetic energy, fully agrees with our simulation results mentioned above, suggesting the consistency and accuracy of our simulations and experiments.

Inorganic polyphosphate: a possible stimulant of bone formation.

Inorganic polyphosphates [Poly(P)] are often distributed in osteoblasts. We undertook the present study to verify the hypothesis that Poly(P) stimulates osteoblasts and facilitates bone formation. The osteoblast-like cell line MC 3T3-E1 was cultured with Poly(P), and gene expression and potential mineralization were evaluated by reverse-transcription polymerase chain-reaction. Alkaline phosphatase activity, von Kossa staining, and resorption pit formation analyses were also determined. The potential role of Poly(P) in bone formation was assessed in a rat alveolar bone regeneration model. Poly(P) induced osteopontin, osteocalcin, collagen 1alpha, and osteoprotegerin expression and increased alkaline phosphatase activity in MC 3T3-E1 cells. Dentin slice pit formation decreased with mouse osteoblast and bone marrow macrophage co-cultivation in the presence of Poly(P). Promotion of alveolar bone regeneration was observed locally in Poly(P)-treated rats. These findings suggest that Poly(P) plays a role in osteoblastic differentiation, activation, and bone mineralization. Thus, local poly(P) delivery may have a therapeutic benefit in periodontal disease.

HSF4, a new member of the human heat shock factor family which lacks properties of a transcriptional activator.

Heat shock transcription factors (HSFs) mediate the inducible transcriptional response of genes that encode heat shock proteins and molecular chaperones. In vertebrates, three related HSF genes (HSF1 to -3) and the respective gene products (HSFs) have been characterized. We report the cloning and characterization of human HSF4 (hHSF4), a novel member of the hHSF family that shares properties with other members of the HSF family yet appears to be functionally distinct. hHSF4 lacks the carboxyl-terminal hydrophobic repeat which is shared among all vertebrate HSFs and has been suggested to be involved in the negative regulation of DNA binding activity. hHSF4 is preferentially expressed in the human heart, brain, skeletal muscle, and pancreas. Transient transfection of hHSF4 in HeLa cells, which do not express hHSF4, results in a constitutively active DNA binding trimer which, unlike other members of the HSF family, lacks the properties of a transcriptional activator. Constitutive overexpression of hHSF4 in HeLa cells results in reduced expression of the endogenous hsp70, hsp90, and hsp27 genes. hHSF4 represents a novel hHSF that exhibits tissue-specific expression and functions to repress the expression of genes encoding heat shock proteins and molecular chaperones.