Rapid and Accurate Measurement of Polarization and Fading of Weak VHF Signals Obliquely Reflected from Sporadic-E Layers

In the E-region of the ionosphere, at heights between 90 and 130 km, thin patches of enhanced ionization occur intermittently. The electron density in these sporadic-E (Es) clouds can sometimes be so high that radio waves with frequencies up to 150 MHz are obliquely reflected. While this phenomenon is well known, the reflection mechanism itself is not well understood. To investigate this question, an experimental system has been developed for accurate polarimetric and fading measurements of 50 MHz radio waves obliquely reflected by mid-latitude Es layers. The overall sensitivity of the system is optimized by reducing environmental electromagnetic noise, giving the ability to observe weak, short-lived 50 MHz Es propagation events. The effect of the ground reflection on observed polarization is analyzed and the induced amplitude and phase biases are compensated for. It is found that accurate measurements are only possible below the pseudo-Brewster angle. To demonstrate the effectiveness of the system, initial empirical results are presented which provide clear evidence of magneto-ionic double refraction

Rapid and Accurate Measurement of Polarization and Fading of Weak VHF Signals Obliquely Reflected from Sporadic-E Layers

In the E-region of the ionosphere, at heights between 90 and 130 km, thin patches of enhanced ionization occur intermittently. The electron density in these sporadic-E (Es) clouds can sometimes be so high that radio waves with frequencies up to 150 MHz are obliquely reflected. While this phenomenon is well known, the reflection mechanism itself is not well understood. To investigate this question, an experimental system has been developed for accurate polarimetric and fading measurements of 50 MHz radio waves obliquely reflected by mid-latitude Es layers. The overall sensitivity of the system is optimized by reducing environmental electromagnetic noise, giving the ability to observe weak, short-lived 50 MHz Es propagation events. The effect of the ground reflection on observed polarization is analyzed and the induced amplitude and phase biases are compensated. It is found that accurate measurements are only possible below the pseudo-Brewster angle. To demonstrate the effectiveness of the system, initial empirical results are presented which provide clear evidence of magneto-ionic double refraction.</p

The Curious Case of Acetaldehyde Phenylhydrazone: Resolution of a 120 Year Old Puzzle where Forms with Vastly Different Melting Points Have the Same Structure

Contains fulltext : 201416.pdf (publisher's version ) (Open Access

Assessing the impact of minimizing arginine conversion in fully defined SILAC culture medium in human embryonic stem cells

We present a fully defined culture system (adapted Essential8 (TM) [E8 (TM)] medium in combination with vitronectin) for human embryonic stem cells that can be used for SILAC purposes. Although a complete incorporation of the labels was observed after 4 days in culture, over 90% of precursors showed at least 10% conversion. To reduce this arginine conversion, E8 (TM) medium was modified by adding (1) L-proline, (2) L-ornithine, (3) N-omega-hydroxy-nor-L-arginine acetate, or by (4) lowering the arginine concentration. Reduction of arginine conversion was best obtained by adding 5 mM L-ornithine, followed by 3.5 mM L-proline and by lowering the arginine concentration in the medium to 99.5 mu M. No major changes in pluripotency and cell amount could be observed for the adapted E8 (TM) media with ornithine and proline. However, our subsequent ion mobility assisted data-independent acquisition (high-definition MS) proteome analysis cautions for ongoing changes in the proteome when aiming at longer term suppression of arginine conversion

The curious case of acetaldehyde phenylhydrazone: resolution of a 120 year old puzzle where forms with vastly different melting points have the same structure

The solid forms of acetaldehyde phenylhydrazone were investigated in detail over a century ago, with curious results: it was reported that a low melting form could be transformed into a high melting form by trace alkali, and the reverse process could be brought about with trace acid. Our reinvestigation of this puzzle with modern instrumentation has shown that all samples, although exhibiting sharp melting points varying from 56 to 101 °C, have identical IR and solid-state NMR spectra and identical crystal structures. NMR studies of the melts provided the key to the understanding of this strange behavior: differently melting samples did so because they initially melted to liquids with different proportions of the Z and E isomers, although given enough time they all tended to the same equilibrium proportion. The leading role of the isomerization rate in the melt was confirmed in cyclic differential scanning calorimetry experiments and accompanying simulations. In the case of polymorphism, different structures melt to the same liquid. In the present case, the same structure melts to different liquids

The Evolution of Disk Winds from a Combined Study of Optical and Infrared Forbidden Lines

We analyze high-resolution (Δv≤10 km s-1) optical and infrared spectra covering the [O I] λ6300 and [Ne II] 12.81 μm lines from a sample of 31 disks in different evolutionary stages. Following work at optical wavelengths, we use Gaussian profiles to fit the [Ne II] lines and classify them into high-velocity component (HVC) or lowvelocity component (LVC) if the line centroid is more or less blueshifted than 30 km s-1 with respect to the stellar radial velocity, respectively. Unlike for the [O I], where an HVC is often accompanied by an LVC, all 17 sources with an [Ne II] detection have either an HVC or an LVC. [Ne II] HVCs are preferentially detected toward high accretors (Ṁacc > 10-8 Me⊙ yr-1), while LVCs are found in sources with low Ṁacc, low [O I] luminosity, and large infrared spectral index (n13-31). Interestingly, the [Ne II] and [O I] LVC luminosities display an opposite behavior with n13-31: as the inner dust disk depletes (higher n13-31), the [Ne II] luminosity increases while the [O I] weakens. The [Ne II] and [O I] HVC profiles are generally similar, with centroids and FWHMs showing the expected behavior from shocked gas in microjets. In contrast, the [Ne II] LVC profiles are typically more blueshifted and narrower than the [O I] profiles. The FWHM and centroid versus disk inclination suggest that the [Ne II] LVC predominantly traces unbound gas from a slow, wide-angle wind that has not lost completely the Keplerian signature from its launching region. We sketch an evolutionary scenario that could explain the combined [O I] and [Ne II] results and includes screening of hard (∼1 keV) X-rays in inner, mostly molecular, MHD winds