145 research outputs found
Development of liquid-assisted grinding (LAG) for the synthesis of hydrogen-bonded and coordination frameworks
A brief overview is given on the use of the mechanochemical
method liquid-assisted grinding as an alternative, clean and a rapid means to synthesise and screen for molecular inclusion and open frameworks based on hydrogen bonds and
coordination bonds
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A mechanochemical strategy for IRMOF assembly based on pre-designed oxo-zinc precursors.
We demonstrate a mechanochemical strategy that allowed the first successful mechanosynthesis of IRMOFs based on an oxo-centred secondary building unit (SBU). The presented study indicates that controlling the acid-base relationship between reagents is key to mechanochemical synthesis of IRMOFs, revealing a pre-assembled oxo-zinc amidate cluster as an efficient precursor for IRMOF mechanosynthesis.The authors would like to acknowledge the project operated within the Foundation for Polish Science Team Programme co-financed by the EU ‘‘European Regional Development Fund’’ TEAM/2011–7/8, and the European Union in the framework of Regional Development Fund through the Joint UW and WUT International PhD Program of Foundation for Polish Science – “Towards Advanced Functional Materials and Novel Devices” (MPD/2010/4) (D.P.) for financial support.This is the accepted manuscript. The final version was published in Chemical Communications and is available at http://pubs.rsc.org/en/Content/ArticleLanding/2015/CC/c4cc09917f#!divAbstract
A Large-Scale FPGA-Based Trigger and Dead-Time Free DAQ System for the Kaos Spectrometer at MAMI
The Kaos spectrometer is maintained by the A1 collaboration at the Mainz
Microtron MAMI with a focus on the study of (e,e'K^+) coincidence reactions.
For its electron-arm two vertical planes of fiber arrays, each comprising
approximately 10 000 fibers, are operated close to zero degree scattering angle
and in close proximity to the electron beam. A nearly dead-time free DAQ system
to acquire timing and tracking information has been installed for this
spectrometer arm. The signals of 144 multi-anode photomultipliers are collected
by 96-channel front-end boards, digitized by double-threshold discriminators
and the signal time is picked up by state-of-the-art F1 time-to-digital
converter chips. In order to minimize background rates a sophisticated trigger
logic was implemented in newly developed Vuprom modules. The trigger performs
noise suppression, signal cluster finding, particle tracking, and coincidence
timing, and can be expanded for kinematical matching (e'K^+) coincidences. The
full system was designed to process more than 4 000 read-out channels and to
cope with the high electron flux in the spectrometer and the high count rate
requirement of the detectors. It was successfully in-beam tested at MAMI in
2009.Comment: Contributed to 17th IEEE Real Time Conference (RT10), Lisbon, 24-28
May 201
Experimental and Theoretical Evaluation of the Stability of True MOF Polymorphs Explains Their Mechanochemical Interconversions.
We provide the first combined experimental and theoretical evaluation of how differences in ligand structure and framework topology affect the relative stabilities of isocompositional (i.e., true polymorph) metal-organic frameworks (MOFs). We used solution calorimetry and periodic DFT calculations to analyze the thermodynamics of two families of topologically distinct polymorphs of zinc zeolitic imidazolate frameworks (ZIFs) based on 2-methyl- and 2-ethylimidazolate linkers, demonstrating a correlation between measured thermodynamic stability and density, and a pronounced effect of the ligand substituent on their stability. The results show that mechanochemical syntheses and transformations of ZIFs are consistent with Ostwald's rule of stages and proceed toward thermodynamically increasingly stable, more dense phases.Support for calorimetry was provided by the U.S. Department of Energy, Grant DE-SC0016573. We acknowledge the financial support of the NSERC Strategic Grant STPGP 463405-14. A.D.K. acknowledges support by the FRQNT Postdoctoral Scholarship. We are grateful for computational support from the UK national high performance computing
service, ARCHER, for which access was obtained via the UKCP consortium and funded by EPSRC Grant Ref EP/K013564/1
Observation of Lambda H-4 hyperhydrogen by decay-pion spectroscopy in electron scattering
At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from
decays of strange systems was performed by electron scattering off a Be-9
target in order to study the ground-state masses of Lambda-hypernuclei.
Positively charged kaons were detected by a short-orbit spectrometer with a
broad momentum acceptance at zero degree forward angles with respect to the
beam, efficiently tagging the production of strangeness in the target nucleus.
In coincidence, negatively charged decay-pions were detected by two independent
high-resolution spectrometers. About 10^3 pionic weak decays of hyperfragments
and hyperons were observed. The pion momentum distribution shows a
monochromatic peak at p_pi ~ 133 MeV/c, corresponding to the unique signature
for the two-body decay of hyperhydrogen Lambda H-4 -> He-4 + pi-, stopped
inside the target. Its binding energy was determined to be B_Lambda = 2.12 +-
0.01 (stat.) +- 0.09 (syst.) MeV with respect to the H-3 + Lambda mass
Exclusive electroproduction of K+ Lambda and K+ Sigma^0 final states at Q^2 = 0.030-0.055 (GeV/c)^2
Cross section measurements of the exclusive p(e,e'K+)Lambda,Sigma^0
electroproduction reactions have been performed at the Mainz Microtron MAMI in
the A1 spectrometer facility using for the first time the Kaos spectrometer for
kaon detection. These processes were studied in a kinematical region not
covered by any previous experiment. The nucleon was probed in its third
resonance region with virtual photons of low four-momenta, Q^2= 0.030-0.055
(GeV/c)^2. The MAMI data indicate a smooth transition in Q^2 from
photoproduction to electroproduction cross sections. Comparison with
predictions of effective Lagrangian models based on the isobar approach reveal
that strong longitudinal couplings of the virtual photon to the N* resonances
can be excluded from these models.Comment: 16 pages, 7 figure
Search for light massive gauge bosons as an explanation of the anomaly at MAMI
A massive, but light abelian U(1) gauge boson is a well motivated possible
signature of physics beyond the Standard Model of particle physics. In this
paper, the search for the signal of such a U(1) gauge boson in
electron-positron pair-production at the spectrometer setup of the A1
Collaboration at the Mainz Microtron (MAMI) is described. Exclusion limits in
the mass range of 40 MeV up to 300 MeV with a sensitivity in the mixing
parameter of down to are presented. A large
fraction of the parameter space has been excluded where the discrepancy of the
measured anomalous magnetic moment of the muon with theory might be explained
by an additional U(1) gauge boson.Comment: 4 pages, 3 figure
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