765 research outputs found
Calculations on the production and use of superfine holographic X-ray gratings for astrophysical observations
Superfine holograhic X-ray gratings may be produced by transferring onto metal an interference pattern generated by two branches of a sufficiently coherent X-ray beam, emitted in the form of synchrotron radiation from high energy electron storage rings. Generation of the coherent beam requires restrictions on the beam size. A calculation is presented which allows an exact evaluation of this restriction. The effect of defocusing optics on the expected resolution is also studied
Feasibility of coherent X-ray production by X-ray pumping
It is suggested that coherent X-rays can be produced by inverting the electron population in a suitable target, such as Li, through irradiation with X-rays generated by fast electrons traversing an electromagnetic field (as in a storage ring). Conditions to be satisfied by target and radiation parameters are stated, and examples given
Finite bias Cooper pair splitting
In a device with a superconductor coupled to two parallel quantum dots (QDs)
the electrical tunability of the QD levels can be used to exploit non-classical
current correlations due to the splitting of Cooper pairs. We experimentally
investigate the effect of a finite potential difference across one quantum dot
on the conductance through the other completely grounded QD in a Cooper pair
splitter fabricated on an InAs nanowire. We demonstrate that the electrical
transport through the device can be tuned by electrical means to be dominated
either by Cooper pair splitting (CPS), or by elastic co-tunneling (EC). The
basic experimental findings can be understood by considering the energy
dependent density of states in a QD. The reported experiments add
bias-dependent spectroscopy to the investigative tools necessary to develop
CPS-based sources of entangled electrons in solid-state devices.Comment: 4 pages, 4 figure
Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts
Advanced synthesis of semiconductor nanowires (NWs) enables their application
in diverse fields, notably in chemical and electrical sensing, photovoltaics,
or quantum electronic devices. In particular, Indium Arsenide (InAs) NWs are an
ideal platform for quantum devices, e.g. they may host topological Majorana
states. While the synthesis has been continously perfected, only few techniques
were developed to tailor individual NWs after growth. Here we present three wet
chemical etch methods for the post-growth morphological engineering of InAs NWs
on the sub-100 nm scale. The first two methods allow the formation of
self-aligned electrical contacts to etched NWs, while the third method results
in conical shaped NW profiles ideal for creating smooth electrical potential
gradients and shallow barriers. Low temperature experiments show that NWs with
etched segments have stable transport characteristics and can serve as building
blocks of quantum electronic devices. As an example we report the formation of
a single electrically stable quantum dot between two etched NW segments.Comment: 9 pages, 5 figure
Optimal administration of bronchodilators with valved holding chambers in preschool children: a review of literature
Our aim was to synthesize the published literature on factors that potentially affect the delivery of bronchodilators using valved holding chambers (VHC) in preschool children. We also aimed to identify those attributes that are not yet incorporated or clearly stated in the guidelines and those topics that are still lacking sufficient data. There is strong evidence supporting several recommendations in current guidelines. Based on present knowledge, bronchodilators should be delivered by VHC administering each puff separately. Face mask should be omitted as soon as the child can hold the mouthpiece of the VHC tightly between the lips and teeth. Based on the review, we suggest adding a specific note to current guidelines about the effect of chamber volume and the impact of co-operation during drug administration. Calming the child and securing a tight face-to-mask seal is critical for successful drug delivery. There is not enough evidence to make specific recommendations on the most reliable VHC and face mask for children. There is an urgent need for studies that evaluate and compare the effectiveness of VHCs in various clinical settings in wide age-groups and respiratory patterns. In addition, there is insufficient data on ideal chamber volume, material, and effective antistatic treatment. What is Known: Valved holding chambers (VHC) should not be considered interchangeable when used with pressurized metered dose inhalers (pMDI). Drug delivery is influenced by VHC volume, aerodynamic and electrostatic properties; mask fit; respiratory pattern and co-operation during inhalation; and the number of puffs actuated. What is New: The impact of co-operation, VHC volume, and good mask-to-face fit during drug inhalation is not stressed enough in the guidelines. Studies are urgently needed to evaluate the effectiveness of different VHCs in various clinical settings focusing on VHC electrostatic properties, respiratory patters, face masks, and ideal pMDI+VHC combinations.Peer reviewe
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