Organs from animals for man

In the following review some of the problems of xenotransplantation shall be discussed, based on the few experimental data available so far and on reports in the literature describing investigations which may be of importance for xenotransplantation. The impact of gravity on the upright posture of man versus almost all other mammals, the dysfunction between enzymes and hormones in different species and the lack of interactions between interleukins, cytokines and vasoactive substances will be taken into consideration. The question must be asked whether different levels of carrier molecules or serum proteins play a role in the physiological network. Even though the development of transgenic animals or other imaginative manipulations may lead to the acceptance of any type of xenografted organ, it has to be established for how long the products of the xenografts are able to act in the multifactorial orchestra. We are far from understanding xenogeneic molecular mechanisms involved in toxicity, necrosis and apoptosis or even reperfusion injury and ischemia in addition to the immediate mechanisms of the hyperacute xenogeneic rejection. Here, cell adhesion, blood clotting and vasomotion collide and bring micro-and macrocirculation to a standstill. All types of xenogeneic immunological mechanisms studied so far were found to have a more serious impact than those seen in allogeneic transplantation. In addition we are now only beginning to understand that so-called immunological parameters in allogeneic mechanisms act also in a true physiological manner in the xenogeneic situation. These molecular mechanisms occur behind the curtain of hyperacute, accelerated, acute or chronic xenograft rejection of which only some folds have been lifted to allow glimpses of part of the total scene. Other obstacles are likely to arise when long-term survival is achieved. These obstacles include retroviral infections, transfer of prions and severe side effects of the massive immunosuppression which will be needed. Moral, ethical and religious concerns are under debate and the species-specific production of proteins of the foreign donor species developed for clinical use suddenly appears to be a greater problem than anticipated

Assessment of mechanical properties and microstructure characterizing techniques in their ability to quantify amount of cold work in 316l alloy

Stress corrosion cracking (SCC) behavior is a matter of concern for structural materials, namely, stainless steels and nickel alloys, in nuclear power plants. High levels of cold work (CW) have shown to both reduce crack initiation times and increase crack growth rates. Cold working has numerous effects on a material, including changes in microstructure, mechanical properties, and residual stress state, yet it is typically reported as a simple percent change in geometry. There is need to develop a strategy for quantitative assessment of cold-work level in order to better understand stress corrosion cracking test data. Five assessment techniques, commonly performed alongside stress corrosion cracking testing (optical microscopy (OM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), tensile testing, and hardness testing) are evaluated with respect to their ability to quantify the level of CW in a component. The test material is stainless steel 316L that has been cold-rolled to three conditions: 0%, 20%, and 30% CW. Measurement results for each assessment method include correlation with CW condition and repeatability data. Measured values showed significant spatial variation, illustrating that CW level is not uniform throughout a component. Mechanical properties (tensile testing, hardness) were found to correlate most linearly with the amount of imparted CW

Optimizing Stimulation and Analysis Protocols for Neonatal fMRI

The development of brain function in young infants is poorly understood. The core challenge is that infants have a limited behavioral repertoire through which brain function can be expressed. Neuroimaging with fMRI has great potential as a way of characterizing typical development, and detecting abnormal development early. But, a number of methodological challenges must first be tackled to improve the robustness and sensitivity of neonatal fMRI. A critical one of these, addressed here, is that the hemodynamic response function (HRF) in pre-term and term neonates differs from that in adults, which has a number of implications for fMRI. We created a realistic model of noise in fMRI data, using resting-state fMRI data from infants and adults, and then conducted simulations to assess the effect of HRF of the power of different stimulation protocols and analysis assumptions (HRF modeling). We found that neonatal fMRI is most powerful if block-durations are kept at the lower range of those typically used in adults (full on/off cycle duration 25-30s). Furthermore, we show that it is important to use the age-appropriate HRF during analysis, as mismatches can lead to reduced power or even inverted signal. Where the appropriate HRF is not known (for example due to potential developmental delay), a flexible basis set performs well, and allows accurate post-hoc estimation of the HRF

Diffusion Enhancement in a Periodic Potential under High-Frequency Space-Dependent Forcing

We study the long-time behavior of underdamped Brownian particle moving through a viscous medium and in a systematic potential, when it is subjected to a space-dependent high-frequency periodic force. When the frequency is very large, much larger than all other relevant system-frequencies, there is a Kapitsa time-window wherein the effect of frequency dependent forcing can be replaced by a static effective potential. Our new analysis includes the case when the forcing, in addition to being frequency-dependent, is space-dependent as well. The results of the Kapitsa analysis then lead to additional contributions to the effective potential. These are applied to the numerical calculation of the diffusion coefficient (D) for a Brownian particle moving in a periodic potential. Presented are numerical results, which are in excellent agreement with theoretical predictions and which indicate a significant enhancement of D due to the space-dependent forcing terms. In addition we study the transport property (current) of underdamped Brownian particles in a ratchet potential.Comment: RevTex 6 pages, 5 figure

Symmetry of two terminal, non-linear electric conduction

The well-established symmetry relations for linear transport phenomena can not, in general, be applied in the non-linear regime. Here we propose a set of symmetry relations with respect to bias voltage and magnetic field for the non-linear conductance of two-terminal electric conductors. We experimentally confirm these relations using phase-coherent, semiconductor quantum dots.Comment: 4 pages, 4 figure

High-fidelity preparation, gates, memory and readout of a trapped-ion quantum bit

We implement all single-qubit operations with fidelities significantly above the minimum threshold required for fault-tolerant quantum computing, using a trapped-ion qubit stored in hyperfine "atomic clock" states of $^{43}$Ca$^+$. We measure a combined qubit state preparation and single-shot readout fidelity of 99.93%, a memory coherence time of $T^*_2=50$ seconds, and an average single-qubit gate fidelity of 99.9999%. These results are achieved in a room-temperature microfabricated surface trap, without the use of magnetic field shielding or dynamic decoupling techniques to overcome technical noise.Comment: Supplementary Information included. 6 nines, 7 figures, 8 page

Microwave control electrodes for scalable, parallel, single-qubit operations in a surface-electrode ion trap

We propose a surface ion trap design incorporating microwave control electrodes for near-field single-qubit control. The electrodes are arranged so as to provide arbitrary frequency, amplitude and polarization control of the microwave field in one trap zone, while a similar set of electrodes is used to null the residual microwave field in a neighbouring zone. The geometry is chosen to reduce the residual field to the 0.5% level without nulling fields; with nulling, the crosstalk may be kept close to the 0.01% level for realistic microwave amplitude and phase drift. Using standard photolithography and electroplating techniques, we have fabricated a proof-of-principle electrode array with two trapping zones. We discuss requirements for the microwave drive system and prospects for scalability to a large two-dimensional trap array.Comment: 8 pages, 6 figure