Tris(dipivalomethanato)holmium Induced NMR Shifts

Paramagnetic complexes of praseodymium and europium with 1,1,l,2,2,3,3- -heptafluoro-7, 7 ~dimethyl-4,6-octanedione [Pr(fod)3 and Eu(fod)3]1 and with 2,2,6,6-tetramethyl-3,5-heptanedione [Pr(DPM)3 and Eu(DPM)3] or sometimes ab:breviated as [Pr(tmhd)3 and Eu(tmhd)3]Z--5 have shown to !be very useful NMR shift reagents which can greatly s~mplify spectra of compounds having functional gro1ups with lone pair electrons. The only other lanthanide oormplex used for this :purpose was Yb(DPM)3 6>7 • However, Yb(DPM)3 exhibited a shift power between that of Pr(DPM)3 and Eu(DPM)3 and also strong line broadening8 and therefore did not offer any substantial advantage

Unconventional spin density wave in Bechgaard salt (TMTSF)2NO3

Among many Bechgaard salts, TMTSF2NO3 exhibits very anomalous low temperature properties. Unlike conventional spin density wave (SDW), TMTSF2NO3 undergoes the SDW transition at \T_SDW\approx 9.5 K and the low temperature quasiparticle excitations are gapless. Also, it is known that TMTSF2NO3 does not exhibit superconductivity even under pressure, while FISDW is found in TMTSF2NO3 only for P=8.5 kbar and B>20 T. Here we shall show that both the angle dependent magnetoresistance data and the nonlinear Hall resistance of TMTSF2NO3 at ambient pressure are interpreted satisfactory in terms of unconventional spin density wave (USDW). Based on these facts, we propose a new phase diagram for Bechgaards salts.Comment: 4 pages, 4 figs, RevTe

LQR distributed cooperative control of a formation of low-speed experimental UAVs

The paper presents a cooperative scheme for controlling arbitrary formations of low speed experimental UAVs based on a distributed LQR design methodology. Each UAV acts as an independent agent in the formation and its dynamics are described by a 6-DOF (degrees of freedom) nonlinear model. This is linearized for control design purposes around an operating point corresponding to straight flight conditions and simulated only for longitudinal motion. It is shown that the proposed controller stabilizes the overall formation and can control effectively the nonlinear multi-agent system. Also, it is shown via numerous simulations that the system provides reference tracking and that is robust to environmental disturbances such as nonuniform wind gusts acting on a formation of four UAVs and to the loss of communication between two neighbouring UAVs

Origin of Low-Energy Excitations in Charge-Ordered Manganites

The low-energy excitations in the charge-ordered phase of polycrystalline La0.25Ca0.75MnO3 are explored by frequency-domain terahertz spectroscopy. In the frequency range from 4 cm^-1 to 700 cm^-1 (energies 0.4 meV to 90 meV) and at temperatures down to 5 K, we do not detect any feature that can be associated with the collective response of the spatially modulated charge continuum. In the antiferromagnetically ordered phase, broad absorption bands appear in the conductivity and permittivity spectra around 30 cm^-1 and 100 cm^-1 which are assigned to former acoustic phonons optically activated due to a fourfold superstructure in the crystal lattice. Our results indicate that characteristic energies of collective excitations of the charge-ordered phase in La0:25Ca0:75MnO3, if any, lie below 1 meV. At our lowest frequencies of only few wavenumbers a strong relaxation is observed above 100 K connected to the formation of the charge-ordered state.Comment: 5 pages, 3 figure

Delphi survey on the most promising areas and methods to improve systematic reviews' production and updating

BACKGROUND: Systematic reviews (SRs) are invaluable evidence syntheses, widely used in biomedicine and other scientific areas. Tremendous resources are being spent on the production and updating of SRs. There is a continuous need to automatize the process and use the workforce and resources to make it faster and more efficient. METHODS: Information gathered by previous EVBRES research was used to construct a questionnaire for round 1 which was partly quantitative, partly qualitative. Fifty five experienced SR authors were invited to participate in a Delphi study (DS) designed to identify the most promising areas and methods to improve the efficient production and updating of SRs. Topic questions focused on which areas of SRs are most time/effort/resource intensive and should be prioritized in further research. Data were analysed using NVivo 12 plus, Microsoft Excel 2013 and SPSS. Thematic analysis findings were used on the topics on which agreement was not reached in round 1 in order to prepare the questionnaire for round 2. RESULTS: Sixty percent (33/55) of the invited participants completed round 1; 44% (24/55) completed round 2. Participants reported average of 13.3 years of experience in conducting SRs (SD 6.8). More than two thirds of the respondents agreed/strongly agreed the following topics should be prioritized: extracting data, literature searching, screening abstracts, obtaining and screening full texts, updating SRs, finding previous SRs, translating non-English studies, synthesizing data, project management, writing the protocol, constructing the search strategy and critically appraising. Participants have not considered following areas as priority: snowballing, GRADE-ing, writing SR, deduplication, formulating SR question, performing meta-analysis. CONCLUSIONS: Data extraction was prioritized by the majority of participants as an area that needs more research/methods development. Quality of available language translating tools has dramatically increased over the years (Google translate, DeepL). The promising new tool for snowballing emerged (Citation Chaser). Automation cannot substitute human judgement where complex decisions are needed (GRADE-ing). TRIAL REGISTRATION: Study protocol was registered at https://osf.io/bp2hu/

Cooperative dynamics in charge-ordered state of alpha-(BEDT-TTF)2I3

Electric-field-dependent pulse measurements are reported in the charge-ordered state of alpha-(BEDT-TTF)2I3. At low electric fields up to about 50 V/cm only negligible deviations from Ohmic behavior can be identified with no threshold field. At larger electric fields and up to about 100 V/cm a reproducible negative differential resistance is observed with a significant change in shape of the measured resistivity in time. These changes critically depend whether constant voltage or constant current is applied to the single crystal. At high enough electric fields the resistance displays a dramatic drop down to metallic values and relaxes subsequently in a single-exponential manner to its low-field steady-state value. We argue that such an electric-field induced negative differential resistance and switching to transient states are fingerprints of cooperative domain-wall dynamics inherent to two-dimensional bond-charge density wave with ferroelectric-like nature.Comment: 6 pages, 4 figures, resubmitted to Phys. Rev.

Charge-density wave formation in Sr_{14}Cu_{24}O_{41}

The electrodynamic response of the spin-ladder compound Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ ($x=0, 3, 9$) has been studied from radiofrequencies up to the infrared. At temperatures below 250 K a pronounced absorption peak appears around 12 cm$^{-1}$ in Sr$_{14}$Cu$_{24}$O$_{41}$ for the radiation polarized along the chains/ladders (${\bf E}\parallel {\bf c}$). In addition a strongly temperature dependent dielectric relaxation is observed in the kHz - MHz range. We explain this behavior by a charge density wave which develops in the ladders sub-system and produces a mode pinned at 12 cm$^{-1}$. With increasing Ca doping the mode shifts up in frequency and eventually disappears for $x=9$ because the dimensionality of the system crosses over from one to two dimensions, giving way to the superconducting ground state under pressure.Comment: One name added to author list 4 pages, 2 figures, email: [email protected]

The Impact of EU Norms and Policies on Consumer Protection Enforcement in Serbia

Pursuant to its 2008 Stabilization and Association Agreement governing the process of EU integration, Serbia is obliged to align its consumer protection standards (including those related to enforcement) with those of the EU. This article considers the overall approach to enforcement of consumer law in Serbia, focussing in particular on the extent to which EU enforcement principles have been successfully exported to Serbia and whether the goals of EU consumer policy have been achieved. It argues that the incorporation of EU norms has brought fundamental changes to Serbian enforcement mechanisms at a formal level, such as in relation to mediation processes as well as the introduction of injunctions for the protection of collective consumer interests. In practice, however, the impact of this incorporation is quite limited. A number of factors that restrict the practical effectiveness of the mediation processes and injunctions required by EU law are explored in the article, including weak sanctions, excessive reliance on poorly resourced consumer organizations, absence of a business culture of compliance or a sophisticated and determined consumer protection enforcement culture sufficiently grounded in expertise, as well as an overarching political, legislative, and institutional instability. These factors also undermine the general aim of EU policy to achieve effective consumer protection enforcement in the Serbian context