Polymersomes are bilayer vesicles, self-assembled from amphiphilic block copolymers. They are versatile nanocapsules with adjustable properties, such as flexibility, permeability, size and ...functionality. However, so far no methodological approach to control their shape exists. Here we demonstrate a mechanistically fully understood procedure to precisely control polymersome shape via an out-of-equilibrium process. Carefully selecting osmotic pressure and permeability initiates controlled deflation, resulting in transient capsule shapes, followed by reinflation of the polymersomes. The shape transformation towards stomatocytes, bowl-shaped vesicles, was probed with magnetic birefringence, permitting us to stop the process at any intermediate shape in the phase diagram. Quantitative electron microscopy analysis of the different morphologies reveals that this shape transformation proceeds via a long-predicted hysteretic deflation-inflation trajectory, which can be understood in terms of bending energy. Because of the high degree of controllability and predictability, this study provides the design rules for accessing polymersomes with all possible different shapes.
Abstract The primary reference instruments for neutron fluence measurements used at the Physikalisch-Technische Bundesanstalt are based on the primary standard for neutron measurements which is the ...differential neutron–proton scattering cross section. Such instruments require considerable effort for their operation and analysis. Therefore, routine measurements are carried out using a transfer instrument to facilitate the efficient provision of services to customers. A series of measurements was conducted to compare the transfer device to the primary reference instruments and ensure the traceability of neutron fluence measurements. This resulted in an improved characterisation of the instrument and new analysis procedures. For neutron energies between 144 keV and 14.8 MeV, the ratio of neutron fluence values measured with the primary reference instruments and the transfer instrument deviates from unity by less than the estimated standard measurement uncertainties of 2.6% to 3.2%. At neutron energies between 30 keV and 100 keV, however, the experimental fluence ratios deviate from unity by about 4% which exceeds the estimated uncertainties of 2.5% to 2.9%. At present, the reason for this inconsistency remains unresolved.
Porphyrins, phthalocyanines, and perylenes are compounds with great potential for serving as components of molecular materials that possess unique electronic, magnetic and photophysical properties. ...In general, a highly specific communication between a large number of these chromophores is required in order to express their function to a maximal level, and for this reason it is of importance to construct arrays in which the molecules are organized in well‐defined geometries with respect to their neighbors. This review is an account of some recent efforts to construct highly ordered assemblies of porphyrins, phthalocyanines, and perylenes by means of self‐assembly in solution and on surfaces, and by attaching them to polymeric scaffolds.
Porphyrins, phthalocyanines, and perylenes often serve as building blocks for molecular materials with unique electronic, magnetic, and photophysical properties. Some recent efforts to construct highly organized arrays of these chromophores by means of self‐assembly and by attaching them to polymer scaffolds (see figure) are described.
A disk-shaped molecule with chiral tails is shown to form long fibers of molecular diameter and micrometer length by self-assembly in chloroform. The molecules are derived from crown ethers and ...contain a phthalocyanine ring. In the fibers, they have a clockwise, staggered orientation that leads to an overall right-handed helical structure. These structures, in turn, self-assemble to form coiled-coil aggregates with left-handed helicity. Addition of potassium ions to the fibers leaves their structure intact but blocks the transfer of the chirality from the tails to the cores, leading to loss of the helicity of the fibers. These tunable chiral materials have potential in optoelectronic applications and as components in sensor devices.
In standard monoenergetic ISO neutron fields, the neutron yield of neutron-producing reactions was measured in combination with the prompt photon yield, including photon energies up to 10 MeV, for ...the purpose of comparing the two yields. Separating the photons produced by the target (direct photons) from those generated by secondary neutron reactions was achieved using the time-of-flight method. Photon and neutron ambient dose equivalent values were calculated from measured spectral energy distributions. Quasi monoenergetic neutron fields are needed to systematically test the response of measuring instruments to neutron radiation. For this reason, ISO has defined a number of reference neutron radiation fields covering a wide energy range up to 19 MeV. Because neutron detectors may also be affected by photon radiation, the photon fluence in the ISO neutron fields has to be known. This work focuses on quasi monoenergetic accelerator-produced neutron fields in the energy range of 24 keV to 19 MeV.
This article reports the measurement of the ionization quenching factor in germanium for nuclear recoil energies in the keV range. Precise knowledge of this factor in this energy range is highly ...relevant for coherent elastic neutrino-nucleus scattering and low mass dark matter searches with germanium-based detectors. Nuclear recoils were produced in a thin high-purity germanium target with a very low energy threshold via irradiation using monoenergetic neutron beams. The energy dependence of the ionization quenching factor was directly measured via kinematically constrained coincidences with surrounding liquid scintillator based neutron detectors. The systematic uncertainties of the measurements are discussed in detail. With measured quenching factors between 0.16 and 0.23 in the 0.4 keV
nr
to 6.3 keV
nr
energy range, the data are compatible with the Lindhard theory with a parameter
k
of 0.162
±
0.004
(stat + sys).
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Stomatocytes are polymersomes with an infolded bowl-shaped architecture. This internal cavity is connected to the outside environment via a small 'mouth' region. Stomatocytes are assembled from ...diamagnetic amphiphilic block-copolymers with a highly anisotropic magnetic susceptibility, which permits to magnetically align and deform the polymeric self-assemblies. Here we show the reversible opening and closing of the mouth region of stomatocytes in homogeneous magnetic fields. The control over the size of the opening yields magneto-responsive supramolecular valves that are able to reversibly capture and release cargo. Furthermore, the increase in the size of the opening is gradual and starts at fields below 10 T, which opens the possibility of using these structures for delivery and nanoreactor applications.
Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Because of their unique coherence properties, Bose-Einstein condensates ...are ideal sources for an atom interferometer in extended free fall. In this Letter we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far field of a double slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.
Characterization of a cubic EJ-309 liquid scintillator detector Tomanin, A.; Paepen, J.; Schillebeeckx, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2014, Letnik:
756
Journal Article
Recenzirano
A cubic EJ-309 liquid scintillator of 10cm width has been characterized for its response to γ-rays and neutrons. Response functions to γ-rays were measured with calibrated radionuclide γ-ray sources ...in the energy range from 400keV to 6MeV. Response functions for neutrons were obtained from measurements at the PTB Van de Graaff accelerator with quasi-monoenergetic neutron beams in the energy range from 500keV to 2.7MeV, and at the PTB cyclotron with time-of-flight (TOF) measurements in the energy range from 2.5 to 14MeV. The light output and resolution functions for electrons and protons were derived by a least squares adjustment to experimental data using theoretical response functions determined with Monte Carlo simulations. The simulated response function for neutron was validated by results of measurements with an AmBe neutron source which was characterized for its total neutron intensity. The results indicate that the cubic EJ-309 detector is suitable for use in mixed γ-ray and neutron fields.
•The paper reports the characterization of a cubic EJ-309 liquid scintillator detector.•The light output and resolution functions for electron and proton are described.•Experimental response function were obtained with gamma sources and neutron beams.•Theoretical response functions were derived by Monte Carlo simulations.•The neutron response function was validated by measurement with an AmBe source.
Diseases that are linked to defective genes or mutations can in principle be cured by gene therapy, in which damaged or absent genes are either repaired or replaced by new DNA in the nucleus of the ...cell. Related to this, disorders associated with elevated protein expression levels can be treated by RNA interference
the delivery of siRNA to the cytoplasm of cells. Polynucleotides can be brought into cells by viruses, but this is not without risk for the patient. Alternatively, DNA and RNA can be delivered by transfection,
by non-viral vector systems such as cationic surfactants, which are also referred to as cationic lipids. In this review, recent progress on cationic lipids as transfection vectors will be discussed, with special emphasis on geminis, surfactants with 2 head groups and 2 tails connected by a spacer.
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