145 research outputs found
Light-induced dipolar spectroscopy - A quantitative comparison between LiDEER and LaserIMD
Nanometric distance measurements with EPR spectroscopy yield crucial
information on the structure and interactions of macromolecules in complex
systems. The range of suitable spin labels for such measurements was recently
expanded with a new class of light-inducible labels: the triplet state of
porphyrins. Importantly, accurate distance measurements between a triplet label
and a nitroxide have been reported with two distinct light-induced spectroscopy
techniques, (light-induced) triplet-nitroxide DEER (LiDEER) and laser-induced
magnetic dipole spectroscopy (LaserIMD). In this work, we set out to
quantitatively compare the two techniques under equivalent conditions at Q
band. Since we find that LiDEER using a rectangular pump pulse does not reach
the high modulation depth that can be achieved with LaserIMD, we further
explore the possibility of improving the LiDEER experiment with chirp inversion
pulses. LiDEER employing a broadband pump pulse results in a drastic
improvement of the modulation depth. The relative performance of chirp LiDEER
and Laser-IMD in terms of modulation-to-noise ratio is found to depend on the
dipolar evolution time: While LaserIMD yields higher modulation-to-noise ratios
than LiDEER at short dipolar evolution times ({\tau}=2 {\mu}s), the high phase
memory time of the triplet spins causes the situation to revert at {\tau}=6
{\mu}s.Comment: 9 pages, 4 figures and supporting information (18 pages, 11 figures
Adapting a practical EPR dosimetry protocol to measure output factors in small fields with alanine.
PURPOSE
Modern radiotherapy techniques often deliver small radiation fields. In this work, a practical Electron Paramagnetic Resonance (EPR) dosimetry protocol is adapted and applied to measure output factors (OF) in small fields of a 6 MV radiotherapy system. Correction factors and uncertainties are presented and OFs are compared to the values obtained by following TRS-483 using an ionization chamber (IC).
METHODS
Irradiations were performed at 10 cm depth inside a water phantom positioned at 90 cm source to surface distance with a 6 MV flattening filter free photon beam of a Halcyon radiotherapy system. OFs for different nominal field sizes (1 × 1, 2 × 2, 3 × 3, 4 × 4, normalized to 10 × 10 cm2 ) were determined with a PinPoint 3D (PTW 31022) IC following TRS-483 as well as with alanine pellets with a diameter of 4 mm and a height of 2.4 mm. EPR readout was performed with a benchtop X-band spectrometer. Correction factors due to volume averaging and due to positional uncertainties were derived from 2D film measurements.
RESULTS
OFs obtained from both dosimeter types agreed within 0.7% after applying corrections for the volume averaging effect. For the used alanine pellets, volume averaging correction factors of 1.030(2) for the 1 × 1 cm2 field and <1.002 for the larger field sizes were determined. The correction factor for positional uncertainties of 1 mm was in the order of 1.018 for the 1 × 1 cm2 field. Combined relative standard uncertainties uc for the OFs resulting from alanine measurements were estimated to be below 1.5% for all field sizes. For IC measurements, uc was estimated to be below 1.0%.
CONCLUSIONS
A practical EPR dosimetry protocol is adaptable for precisely measuring OFs in small fields down to 1 × 1 cm2 . It is recommended to consider the effect of positional uncertainties for field sizes <2 × 2 cm2
Reproducción humana asistida : los problemas que suscita desde la bioética y el derecho
El artículo trata de los problemas éticos y jurídicos que surgen a raíz de la puesta en práctica de técnicas de reproducción asistida, al querer determinar la paternidad o poder elegir el sexo de un embrión viable, entre otros.The article deals with the ethical and juridical problems derived from the implementation of assisted reproduction techniques in determining paternity a the sex of au embryo, among other questions
Molecular quantum spin network controlled by a single qubit
Scalable quantum technologies will require an unprecedented combination of
precision and complexity for designing stable structures of well-controllable
quantum systems. It is a challenging task to find a suitable elementary
building block, of which a quantum network can be comprised in a scalable way.
Here we present the working principle of such a basic unit, engineered using
molecular chemistry, whose control and readout are executed using a nitrogen
vacancy (NV) center in diamond. The basic unit we investigate is a synthetic
polyproline with electron spins localized on attached molecular sidegroups
separated by a few nanometers. We demonstrate the readout and coherent
manipulation of very few () of these electronic spin systems
and access their direct dipolar coupling tensor. Our results show, that it is
feasible to use spin-labeled peptides as a resource for a molecular-qubit based
network, while at the same time providing simple optical readout of single
quantum states through NV-magnetometry. This work lays the foundation for
building arbitrary quantum networks using well-established chemistry methods,
which has many applications ranging from mapping distances in single molecules
to quantum information processing.Comment: Author name typ
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