259 research outputs found
Charge Order in the Falicov-Kimball Model
We examine the spinless one-dimensional Falicov-Kimball model (FKM) below
half-filling, addressing both the binary alloy and valence transition
interpretations of the model. Using a non-perturbative technique, we derive an
effective Hamiltonian for the occupation of the localized orbitals, providing a
comprehensive description of charge order in the FKM. In particular, we uncover
the contradictory ordering roles of the forward-scattering and backscattering
itinerant electrons: the latter are responsible for the crystalline phases,
while the former produces the phase separation. We find an Ising model
describes the transition between the phase separated state and the crystalline
phases; for weak-coupling we present the critical line equation, finding
excellent agreement with numerical results. We consider several extensions of
the FKM that preserve the classical nature of the localized states. We also
investigate a parallel between the FKM and the Kondo lattice model, suggesting
a close relationship based upon the similar orthogonality catastrophe physics
of the associated single-impurity models.Comment: 39 pages, 6 figure
Investigation of the influence of hybrid layers on the life time of hot forging dies
The paper deals with the issues related in the process of drop forging with special attention paid to the durability of forging tools. It presents the results of industrial investigation of the influence of hybrid layers on hot forging dies. The effectiveness of hybrid layers type nitrided layer/PVD coating applied for extending the life of forging tools whose working surfaces are exposed to such complex exploitation conditions as, among others, cyclically varying high thermal and mechanical loads, as well as intensive abrasion at raised temperature. The examination has been performed on a set of forging tools made of Unimax steel and intended for forging steel rings of gear box synchronizer in the factory FAS in Swarzedz (Poland)
Predicting the surface roughness in the dry machining of duplex stainless steel (DSS)
This paper examines the influence of cutting parameters, namely cutting speed, feed and depth of cut onto surface roughness after DSS turning process. The study included developing a mathematical model to determine the surface roughness. Verification research has been carried out on CNC lathe; hence the test plan has been adjusted to the possibility of programmable machines controlling GE Fanuc Series 0-T. The comparison of results obtained by given experimental plan was performed in industrial company
Growth and magnetic properties of multiferroic LaxBi1-xMnO3 thin films
A comparative study of LaxBi1-xMnO3 thin films grown on SrTiO3 substrates is reported. It is shown that these films grow epitaxially in a narrow pressure-temperature range. A detailed structural and compositional characterization of the films is performed within the growth window. The structure and the magnetization of this system are investigated. We find a clear correlation between the magnetization and the unit-cell volume that we ascribe to Bi deficiency and the resultant introduction of a mixed valence on the Mn ions. On these grounds, we show that the reduced magnetization of LaxBi1-xMnO3 thin films compared to the bulk can be explained quantitatively by a simple model, taking into account the deviation from nominal composition and the Goodenough-Kanamori-Anderson rules of magnetic interactions
Predicting the surface roughness in the dry machining of duplex stainless steel (DSS)
This paper examines the influence of cutting parameters, namely cutting speed, feed and depth of cut onto surface roughness after DSS turning process. The study included developing a mathematical model to determine the surface roughness. Verification research has been carried out on CNC lathe; hence the test plan has been adjusted to the possibility of programmable machines controlling GE Fanuc Series 0-T. The comparison of results obtained by given experimental plan was performed in industrial company
Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2
Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction,
magnetic susceptibility, magnetization, electrical resistivity, and specific
heat measurements carried out in wide temperature and magnetic field ranges.
Moreover, the electronic structure of the compound was studied at room
temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The
physical properties were analyzed in terms of crystalline electric field and
compared with results of ab-initio band structure calculations performed within
the density functional theory approach. The compound was found to crystallize
in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma -- No.74,
Pearson symbol: oI24) with the lattice parameters: a = 7.1330(14) A, b =
9.7340(19) A, and c = 5.6040(11) A. Analysis of the magnetic and XPS data
revealed the presence of well localized magnetic moments of trivalent cerium
ions. All physical properties were found to be highly anisotropic over the
whole temperature range studied, and influenced by exceptionally strong
crystalline electric field with the overall splitting of the 4f1 ground
multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic
moments at TN = 4.70(1)K and their subsequent spin rearrangement at Tt =
4.48(1) K manifest themselves as distinct anomalies in the temperature
characteristics of all investigated physical properties and exhibit complex
evolution in an external magnetic field. A tentative magnetic B-T phase
diagram, constructed for B parallel to the b-axis being the easy magnetization
direction, shows very complex magnetic behavior of CeRh3Si2, similar to that
recently reported for an isostructural compound CeIr3Si2. The electronic band
structure calculations corroborated the antiferromagnetic ordering of the
cerium magnetic moments and well reproduced the experimental XPS valence band
spectrum.Comment: 32 pages, 12 figures, to appear in Physical Review
Stripe phases in the two-dimensional Falicov-Kimball model
The observation of charge stripe order in the doped nickelate and cuprate
materials has motivated much theoretical effort to understand the underlying
mechanism of the stripe phase. Numerical studies of the Hubbard model show two
possibilities: (i) stripe order arises from a tendency toward phase separation
and its competition with the long-range Coulomb interaction or (ii) stripe
order inherently arises as a compromise between itinerancy and magnetic
interactions. Here we determine the restricted phase diagrams of the
two-dimensional Falicov-Kimball model and see that it displays rich behavior
illustrating both possibilities in different regions of the phase diagram.Comment: (5 pages, 3 figures
Phase separation due to quantum mechanical correlations
Can phase separation be induced by strong electron correlations? We present a
theorem that affirmatively answers this question in the Falicov-Kimball model
away from half-filling, for any dimension. In the ground state the itinerant
electrons are spatially separated from the classical particles.Comment: 4 pages, 1 figure. Note: text and figure unchanged, title was
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Application of new lysine-based peptide dendrimers D3K2 and D3G2 for gene delivery: Specific cytotoxicity to cancer cells and transfection in vitro
In order to enhance intracellular uptake and accumulation of therapeutic nucleic acids for improved gene therapy methods, numerous delivery vectors have been elaborated. Based on their origin, gene carriers are generally classified as viral or non-viral vectors. Due to their significantly reduced immunogenicity and highly optimized methods of synthesis, nanoparticles (especially those imitating natural biomolecules) constitute a promising alternative for virus-based delivery devices. Thus, we set out to develop innovative peptide dendrimers for clinical application as transfection agents and gene carriers. In the present work we describe the synthesis of two novel lysine-based dendritic macromolecules (D3K2 and D3G2) and their initial characterization for cytotoxicity/genotoxicity and transfection potential in two human cell line models: cervix adenocarcinoma (HeLa) and microvascular endothelial (HMEC-1). This approach allowed us to identify more cationic D3K2 as potent delivery agent, being able to increase intracellular accumulation of large nucleic acid molecules such as plasmids. Moreover, the dendrimers exhibited specific cytotoxicity towards cancer cell line without showing significant toxic effects on normal cells. These observations are promising prognosis for future clinical application of this type of nanoparticles. © 2019 The Author
Photoconductivity in BiFeO3 thin films
The optical properties of epitaxial BiFeO3 thin films have been characterized in the visible range. Variable temperature spectra show an absorption onset near 2.17 eV, a direct gap (2.667±0.005 eV at 300 K), and charge transfer excitations at higher energy. Additionally, we report photoconductivity in BiFeO3 films under illumination from a 100 mW/cm2 white light source. A direct correlation is observed between the magnitude of the photoconductivity and postgrowth cooling pressure. Dark conductivities increased by an order of magnitude when comparing films cooled in 760 and 0.1 Torr. Large increases in photoconductivity are observed in light
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