354 research outputs found
Kinetics of gas emission from aluminosilicates used as a relaxing additive for moulding and core sands
The article presents the results of gas emissions generated during heating of mineral additives – aluminosilicates (perlite ore and vermiculite). The test on a laboratory stand for a 1 g sample at 1 000 °C was carried out. It has been shown, that there is a correlation between the degree of fragmentation and the amount of gas generated. The finest fraction of perlite ore caused a similar quantitative gas emission as ground vermiculite. The presence of additives in molding sands, regardless of the size of fraction, should not affect the formation of casting defects. The addition of perlite ore and vermiculite does not effect the ecological properties of moulding sand
Investigation of chlorine radical chemistry in the Eyjafjallajkull volcanic plume using observed depletions in non-methane hydrocarbons
As part of the effort to understand volcanic plume composition and chemistry during the eruption of the Icelandic volcano Eyjafjallajkull, the CARIBIC atmospheric observatory was deployed for three special science flights aboard a Lufthansa passenger aircraft. Measurements made during these flights included the collection of whole air samples, which were analyzed for non-methane hydrocarbons (NMHCs). Hydrocarbon concentrations in plume samples were found to be reduced to levels below background, with relative depletions characteristic of reaction with chlorine radicals (Cl). Recent observations of halogen oxides in volcanic plumes provide evidence for halogen radical chemistry, but quantitative data for free halogen radical concentrations in volcanic plumes were absent. Here we present the first observation-based calculations of Cl radical concentrations in volcanic plumes, estimated from observed NMHC depletions. Inferred Cl concentrations were between 1.3 × 10 and 6.6 × 10 Cl cm. The relationship between NMHC variability and local lifetimes was used to investigate the ratio between OH and Cl within the plume, with [OH]/[Cl] estimated to be ∼37. Copyright 2011 by the American Geophysical Union
Conclusions from CDF Results on CP Violation in D^0 \to \pi^+\pi^-, K^+K^- and Future Tasks
Within the Standard Model (SM) one predicts both direct and indirect CP
violation in D^0 \to \pi^+\pi^-, K^+K^- transitions, although the effects are
tiny: Indirect CP asymmetry cannot exceed O(10^{-4}), probably even O(10^{-5});
direct effects are estimated at not larger than 10^{-4}. At B factories direct
and indirect asymmetries have been studied with /\tau_{D^0} ~ 1; no CP
asymmetry was found with an upper bound of about 1%. CDF has shown intriguing
data on CP violation in D^0 \to \pi^+\pi^- [K^+K^-] with /\tau_{D^0} ~ 2.4
[2.65]. Also, CDF has not seen any CP violation. For direct CP asymmetry, CDF
has a sensitivity similar to the combination of the B factories, yet for
indirect CP violation it yields a significantly smaller sensitivity of
a_{cp}^{ind}=(-0.01 +- 0.06_{stat} +- 0.05_{syst})% due to it being based on
longer decay times. New Physics models (NP) like Little Higgs Models with
T-Parity (LHT) can produce an indirect CP asymmetry up to 1%; CDF's findings
thus cover the upper range of realistic NP predictions ~ 0.1 - 1%. One hopes
that LHCb and a Super-Flavour Factory will probe the lower range down to
~0.01%. Such non-ad-hoc NP like LHT cannot enhance direct CP violation
significantly over the SM level in D^0 \to \pi^+\pi^-, K^+K^- and D^{\pm} \to
\pi^{\pm}K^+K^- transitions, but others might well do so.Comment: 11 pages, 1 figure. V2 has minor corrections and corresponds to the
published versio
Exploring oxidative modifications of tyrosine:an update on mechanisms of formation, advances in analysis and biological consequences
Protein oxidation is increasingly recognised as an important modulator of biochemical pathways controlling both physiological and pathological processes. While much attention has focused on cysteine modifications in reversible redox signalling, there is increasing evidence that other protein residues are oxidised in vivo with impact on cellular homeostasis and redox signalling pathways. A notable example is tyrosine, which can undergo a number of oxidative post-translational modifications to form 3-hydroxy-tyrosine, tyrosine crosslinks, 3-nitrotyrosine and halogenated tyrosine, with different effects on cellular functions. Tyrosine oxidation has been studied extensively in vitro, and this has generated detailed information about the molecular mechanisms that may occur in vivo. An important aspect of studying tyrosine oxidation both in vitro and in biological systems is the ability to monitor the formation of oxidised derivatives, which depends on a variety of analytical techniques. While antibody-dependent techniques such as ELISAs are commonly used, these have limitations, and more specific assays based on spectroscopic or spectrometric techniques are required to provide information on the exact residues modified and the nature of the modification. These approaches have helped understanding of the consequences of tyrosine oxidation in biological systems, especially its effects on cell signalling and cell dysfunction, linking to roles in disease. There is mounting evidence that tyrosine oxidation processes are important in vivo and can contribute to cellular pathology
High-spectral-resolution Fabry-Perot interferometers overcome fundamental limitations of present volcanic gas remote sensing techniques
Remote sensing (RS) of volcanic gases has become a central tool for studying volcanic activity. For instance, ultraviolet (UV) skylight spectroscopy with grating spectrographs (GS) enables SO2 (and, under favourable conditions, BrO) quantification in volcanic plumes from autonomous platforms at safe distances. These measurements can serve volcanic monitoring and they cover all stages of volcanic activity in long measurement time series, which substantially contributes to the refinement of theories on volcanic degassing. Infrared (IR) remote sensing techniques are able to measure further volcanic gases (e.g., HF, HCl, CO2, CO). However, the employed Fourier transform spectrometers (FTSs) are intrinsically intricate and, due to limited resolving power or light throughput, mostly rely on either lamps, direct sun, or hot lava as light source, usually limiting measurements to individual field campaigns. We show that many limitations of grating spectrographs and Fourier transform spectrometer measurements can be overcome by Fabry-Perot interferometer (FPI) based spectrograph implementations. Compared to grating spectrographs and Fourier transform spectrometers, Fabry-Perot interferometer spectrographs reach a 1-3 orders of magnitude higher spectral resolution and superior light throughput with compact and stable set-ups. This leads to 1) enhanced sensitivity and selectivity of the spectral trace gas detection, 2) enables the measurement of so far undetected volcanic plume constituents [e.g., hydroxyl (OH) or sulfanyl (SH)], and 3) extends the range of gases that can be measured continuously using the sky as light source. Here, we present measurements with a shoe-box-size Fabry-Perot interferometer spectrograph (resolving power of ca. 150000), performed in the crater of Nyiragongo volcano. By analysing the light of a ultraviolet light emitting diode that is sent through the hot gas emission of an active lava flow, we reach an OH detection limit of about 20 ppb, which is orders of magnitude lower than the mixing ratios predicted by high-temperature chemical models. Furthermore, we introduce example calculations that demonstrate the feasibility of skylight-based remote sensing of HF and HCl in the short-wave infrared with Fabry-Perot interferometer spectrographs, which opens the path to continuous monitoring and data acquisition during all stages of volcanic activity. This is only one among many further potential applications of remote sensing of volcanic gases with high spectral resolution
The Impact of a 4th Generation on Mixing and CP Violation in the Charm System
We study D0-D0 mixing in the presence of a fourth generation of quarks. In
particular, we calculate the size of the allowed CP violation which is found at
the observable level well beyond anything possible with CKM dynamics. We
calculate the semileptonic asymmetry a_SL and the mixing induced CP asymmetry
eta_fS_f which are correlated with each other. We also investigate the
correlation of eta_fS_f with a number of prominent observables in other mesonic
systems like epsilon'/epsilon, Br(K_L -> pi0 nu nu), Br(K+ -> pi+ nu nu),
Br(B_s ->mu+ mu-), Br(B_d -> mu+ mu-) and finally S_psi phi in the B_s system.
We identify a clear pattern of flavour and CP violation predicted by the SM4
model: While simultaneous large 4G effects in the K and D systems are possible,
accompanying large NP effects in the B_d system are disfavoured. However this
behaviour is not as pronounced as found for the LHT and RSc models. In contrast
to this, sizeable CP violating effects in the B_s system are possible unless
extreme effects in eta_fS_f are found, and Br(B_s ->mu+ mu-) can be strongly
enhanced regardless of the situation in the D system. We find that, on the
other hand, S_psi phi > 0.2 combined with the measured epsilon'/epsilon
significantly diminishes 4G effects within the D system.Comment: 22 pages, 23 figures, v2 (references added
Bounds on fourth generation induced Lepton Flavour Violating double insertions in Supersymmetry
We derive bounds on leptonic double mass insertions of the type
in four generational MSSM, using the present
limits on . Two main features distinguish the rates of
these processes in MSSM4 from MSSM3 : (a) tan is restricted to be very
small and (b) the large masses for the fourth generation leptons.
In spite of small , there is an enhancement in amplitudes with
() type insertions which pick up the
mass of the fourth generation lepton, . We find these bounds to be
at least two orders of magnitude more stringent than those in MSSM3.Comment: Latex, 15 pages and 7 figures, Published versio
- …