Competing Antiferromagnetic and Spin-Glass Phases in a Hollandite Structure

We introduce a simple lattice model with Ising spins to explain recent experimental results on spin freezing in a hollandite-type structure. We argue that geometrical frustration of the lattice in combination with nearest-neighbour antiferromagnetic (AFM) interactions is responsible for the appearance of a spin-glass phase in presence of disorder. We investigate this system numerically using parallel tempering. The model reproduces the magnetic behaviour of oxides with hollandite structure, such as $\alpha-\text{MnO}_2$ and presents a rich phenomenology: in absence of disorder three types of ground states are possible, depending on the relative strength of the interactions, namely AFM ordered and two different disordered, macroscopically degenerate families of ground states. Remarkably, for sets of AFM couplings having an AFM ground state in the clean system, there exists a critical value of the disorder for which the ground state is replaced by a spin-glass phase while maintaining all couplings AFM. To the best of our knowledge this is the only existing model that presents this kind of transition with short-range AFM interactions. We argue that this model could be useful to understand the relation between AFM coupling, disorder and the appearance of a spin-glass phase.Comment: 8 pages, 7 figure

Incommensurate, helical spin ground states on the Hollandite lattice

We present a model of classical Heisenberg spins on a Hollandite lattice, which has been developed to describe the magnetic properties of $\alpha$-MnO$_2$ and similar compounds. The model has nearest neighbor interacting spins, however the strength and the sign of spin-spin interactions is anisotropic and depends on the nature of the bonds. Our analysis shows that the Hollandite lattice supports four different incommensurate and helical magnetic ground states depending on the relative strengths and signs of spin-spin interactions. We show that the incommensurate helical ground states appear due to the geometrical frustration present in the model. We demonstrate that each of the four helical incommensurate magnetic phases are continuously connected to four different collinear antiferromagnetic ground states as the strength of spin-spin interaction along some bonds is increased. The present results give support to the presence of helical states that have been previously suggested experimentally for Hollandite compounds. We provide an in-depth analysis of the magnetic form factors for each helical phase and describe how it could be used to identify each of these phases in neutron diffraction experiments.Comment: 11 pages, 8 figure

Tailoring 3D printed cellulose acetate properties produced via direct ink writing: Densification through over-extrusion and evaporation rate control

In this study, we conducted a comprehensive experimental campaign aimed at controlling the final properties of 3D printed cellulose acetate. We equipped a commercial printer with a peristaltic pump to be able to print in a continuous fashion by means of the Direct Ink Writing technique. We investigated the effect of ink concentration and printing parameters on the density, mechanical and functional properties of printed objects. Furthermore, water absorption tests demonstrated the hygroscopic behavior of cellulose acetate, with higher water content in samples with lower densities. The diffusion of water within the polymer network followed Fickian diffusion, with the diffusion coefficient influenced by the density of samples. Overall, this study highlights the importance of printing conditions in achieving desired properties in 3D printed cellulose acetate. The ability to fine-tune the mechanical properties and water absorbance of 3D printed cellulose acetate makes it promising for applications in plant science and bioengineering. Highlights: Cellulose acetate has been 3D printed via Direct Ink Writing. The shear-thinning behavior allows for shape retention during printing. Density of printed samples is strongly controlled by printing parameters. Density of printed parts influences mechanical properties and water absorption

Vacuum 3D printing of highly filled polymeric matrix composites

In this contribution, we have investigated how polymeric matrix composites for aerospace applications are affected, when fabricated at low pressure, by the additive manufacturing process. Commercial filaments have been selected based on their representativeness of materials derived from lunar resources. Standard samples of thermoplastic polymers reinforced by organic fibers and inorganic fillers have been printed inside a vacuum chamber, and their mechanical and thermal properties have been characterized and discussed based on the printing conditions. The reported study represents a preliminary investigation of the potential applicability of the 3D printing technology on highly filled polymers for extraterrestrial applications

Implementasi Supervisi Klinis Oleh Pengawas Untuk Meningkatkan Kinerja Guru Tk Berbasis Permendiknas No. 58 Tahun 2009 Pada Gugus III Kecamatan Buleleng

Penelitian Tindakan Sekolah ini bertujuan untuk meningkatkan kemampuan para guru TK se Gugus III Kecamatan Buleleng dalam menyusun RKM, RKH, melaksanakan proses pembelajaran, dan melaksanakan penilaian yang sesuai dengan Permendiknas No. 58 Tahun 2009 melalui supervisi klinis oleh pengawas. Penelitian dilaksanakan dua siklus dengan subjek sebanyak 27 orang guru. Pengumpulan data dilakukan dengan metode observasi berdasarkan Permendiknas No. 58 Tahun 2009. Data dianalisis secara deskriptif. Indikator keberhasilan penelitian ini adalah 75% dalam kategori baik. Hasil penelitian menunjukkan bahwa terjadi peningkatan dalam menyusun RKM, RKH, melaksanakan proses pembelajaran, dan melaksanakan penilaian yang sesuai dengan Permendiknas No. 58 Tahun 2009. Hal ini terlihat dari tingkat kemampuan guru dalam merencanakan pembelajaran yang meliputi menyusun RKM dan RKH pada siklus I sebesar 75,06% yang tergolong baik, meningkat pada siklus II menjadi 93,25% yang tergolong sangat baik. Tingkat kemampuan guru dalam melaksanakan pembelajaran pada siklus I sebesar 73,57% yang tergolong baik, meningkat pada siklus II menjadi 90,86% yang tergolong sangat baik. Tingkat kemampuan guru dalam melaksanakan penilaian pada siklus I sebesar 74,76% yang tergolong baik, meningkat pada siklus II menjadi 94,13% yang tergolong sangat baik.Kata Kunci : supervisi klinis, kinerja guru, permendiknas no. 58 This classroom action research aims at improving kindergarten teachers\u27 performance in Cluster III of Buleleng Subdistric in making RKM, RKH, implementing teaching-learning process, and doing assessment which are in line with Permendiknas No. 58 Tahun 2009 through clinical supervision. It was done in two cycles with the subject of 27 teachers. The data were collected through observation based on Permendiknas No. 58 Tahun 2009. The data were analyzed descriptively. The expected criteria of this research were 75% or categorized as good. The result of the research shows that there is an improvement in making RKM, RKH, implementing teaching-learning process, and doing assessment which are in line with Permendiknas No. 58 Tahun 2009. It can be seen on the teachers\u27 performance in making RKM and RKH in cycle I which is 75,06% and can be categorized as good improves to 93,25% in cycle II which can be categorized as very good. Teachers\u27 performance in implementing teaching-learning process in cycle I which is 73,57% and can be categorized as good improves to 90,86 in cycle II which can be categorized as very good. Teachers\u27 performance in doing assessment in cycle I which is 74,76% and can be categorized as good improves to 94,13% in cycle II which can be categorized as very good

The carbonyl-lock mechanism underlying non-aromatic fluorescence in biological matter

Challenging the basis of our chemical intuition, recent experimental evidence reveals the presence of a new type of intrinsic fluorescence in biomolecules that exists even in the absence of aromatic or electronically conjugated chemical compounds. The origin of this phenomenon has remained elusive so far. In the present study, we identify a mechanism underlying this new type of fluorescence in different biological aggregates. By employing non-adiabatic ab initio molecular dynamics simulations combined with a data-driven approach, we characterize the typical ultrafast non-radiative relaxation pathways active in non-fluorescent peptides. We show that the key vibrational mode for the non-radiative decay towards the ground state is the carbonyl elongation. Non-aromatic fluorescence appears to emerge from blocking this mode with strong local interactions such as hydrogen bonds. While we cannot rule out the existence of alternative non-aromatic fluorescence mechanisms in other systems, we demonstrate that this carbonyl-lock mechanism for trapping the excited state leads to the fluorescence yield increase observed experimentally, and set the stage for design principles to realize novel non-invasive biocompatible probes with applications in bioimaging, sensing, and biophotonics.Recent experimental evidence shows a new type of intrinsic fluorescence in biomolecules void of aromatic chemical compounds whose origin is unclear. Here, the authors use non-adiabatic AIMD simulations to show a potential carbonyl-lock mechanism originating this phenomenon

Rhodium Nanoparticle Shape Dependence in the Reduction of NO by CO

The shape dependence of the catalytic reduction of nitric oxide by carbon monoxide on rhodium nanopolyhedra and nanocubes was studied from 230 to 270 degrees C. The nanocubes are found to exhibit higher turnover frequency and lower activation energy than the nanopolyhedra. These trends are compared to previous studies on Rh single crystals.Chemistry, PhysicalSCI(E)EI21ARTICLE3-4317-32213

Dioxygen at Biomimetic Single Metal-Atom Sites: Stabilization or Activation? The Case of CoTPyP/Au(111)

By means of a combined experimental and computational approach, we show that a 2D metal\u2013organic framework self-assembled at the Au(111) termination is able to mimic the O2 stabilization and activation mechanisms that are typical of the biochemical environment of proteins and enzymes. 5,10,15,20-tetra(4-pyridyl)21H,23H-porphyrin cobalt(III) chloride (CoTPyP) molecules on Au(111) bind dioxygen forming a covalent bond at the Co center, yielding charge injection into the ligand by exploiting the surface trans-effect. A weakening of the O\u2013O bond occurs, together with the development of a dipole moment, and a change in the molecule\u2019s magnetic moment. Also the bonding geometry is similar to the biological counterpart, with the O2 molecule sitting on-top of the Co atom and the molecular axis tilted by 118\ub0. The ligand configuration lays between the oxo- and the superoxo-species, in agreement with the observed O\u2013O stretching frequency measured in situ at near-ambient pressure conditions

The Influence of the Density Inside a Train Carriage on Passenger Boarding Rate

Passenger alighting and boarding time is an important factor for crowded metros with high-frequency operations. Some operators leave the train doors open until the last passenger boards or passengers voluntarily stop boarding, while others regulate the boarding process. To evaluate whether it is effective to regulate the passenger while boarding or not, this research explores how the density inside the train would influence the passenger boarding rate by conducting a laboratory experiment. The results showed that the passenger boarding rate increased as the density increased, up to approximately 2.5–3.0 passengers/m2. Beyond that point, our results suggested that the boarding rate may have decreased, but the evidence was not conclusive. It is deduced that, under the experimented density (up to around 5 passengers/m2), the density does not have any apparent negative effects on the boarding rate, which implies that there is no strong evidence to recommend passenger boarding regulation