CMB Observations: improvements of the performance of correlation radiometers by signal modulation and synchronous detection

Observation of the fine structures (anisotropies, polarization, spectral distortions) of the Cosmic Microwave Background (CMB) is hampered by instabilities, 1/f noise and asymmetries of the radiometers used to carry on the measurements. Addition of modulation and synchronous detection allows to increase the overall stability and the noise rejection of the radiometers used for CMB studies. In this paper we discuss the advantages this technique has when we try to detect CMB polarization. The behaviour of a two channel correlation receiver to which phase modulation and synchronous detection have been added is examined. Practical formulae for evaluating the improvements are presented.Comment: 18 pages, 3 figures, New Astronomy accepte

Stochastic Electron Acceleration by Temperature Anisotropy Instabilities Under Solar Flare Plasma Conditions

We use 2D particle-in-cell (PIC) plasma simulations to study electron acceleration by electron temperature anisotropy instabilities, assuming magnetic fields ($B$), electron densities ($n_e$) and temperatures ($T_e$) typical of the top of contracting magnetic loops in solar flares. We focus on the long-term effect of $T_{e,\perp} > T_{e,\parallel}$ instabilities by driving the anisotropy growth during the whole simulation time ($T_{e,\perp}$ and $T_{e,\parallel}$ are the temperatures perpendicular and parallel to the field). This is achieved by imposing a shear velocity, which amplifies the field due to magnetic flux freezing, making $T_{e,\perp} > T_{e,\parallel}$ due to electron magnetic moment conservation. We use the initial conditions: $T_e \sim 52$ MK, and $B$ and $n_e$ such that the ratio between the electron cyclotron and plasma frequencies $\omega_{ce}/\omega_{pe}=0.53$. When the anisotropy becomes large enough, oblique, quasi-electrostatic (OQES) modes grow, efficiently scattering the electrons and limiting their anisotropy. After that, when $B$ has grown by a factor $\sim 2-3$ (corresponding to $\omega_{ce}/\omega_{pe}\sim 1.2-1.5$), the unstable modes become dominated by parallel, electromagnetic z (PEMZ) modes. In contrast to the OQES dominated regime, the scattering by PEMZ modes is highly inelastic, producing significant electron acceleration. When the field has grown by a final factor $\sim 4$, the electron energy spectrum shows a nonthermal tail that resembles a power-law of index $\sim$ 2.9, plus a high-energy bump reaching $\sim 300$ keV. Our results suggest a critical role played by $\omega_{ce}/\omega_{pe}$ and $T_e$ in determining the efficiency of electron acceleration by temperature anisotropy instabilities in solar flares.Comment: 11 pages, 9 figure

Magnetic Amplification by Magnetized Cosmic Rays in SNR Shocks

(Abridged) X-ray observations of synchrotron rims in supernova remnant (SNR) shocks show evidence of strong magnetic field amplification (a factor of ~100 between the upstream and downstream medium). This amplification may be due to plasma instabilities driven by shock-accelerated cosmic rays (CRs). One candidate is the cosmic ray current-driven (CRCD) instability (Bell 2004), caused by the electric current of large Larmor radii CRs propagating parallel to the upstream magnetic field. Particle-in-cell (PIC) simulations have shown that the back-reaction of the amplified field on CRs would limit the amplification factor of this instability to less than ~10 in galactic SNRs. In this paper, we study the possibility of further amplification driven near shocks by "magnetized" CRs, whose Larmor radii are smaller than the length scale of the field that was previously amplified by the CRCD instability. We find that additional amplification can occur due to a new instability, driven by the CR current perpendicular to the field, which we term the "perpendicular current-driven instability" (PCDI). We derive the growth rate of this instability, and, using PIC simulations, study its non-linear evolution and saturation. We find that PCDI increases the amplification of the field (amplification factor up to ~45, not including the shock compression) and discuss its observational signatures. Our results strengthen the idea of CRs driving a significant part of the magnetic field amplification observed in SNR shocks.Comment: 14 pages, 10 figures; submitted to Ap

Stochastic Ion Acceleration by the Ion-cyclotron Instability in a Growing Magnetic Field

Using 1D and 2D particle-in-cell (PIC) simulations of a plasma with a growing magnetic field $\vec{B}$, we show that ions can be stochastically accelerated by the ion-cyclotron (IC) instability. As $\vec{B}$ grows, an ion pressure anisotropy $p_{\perp,i} > p_{||,i}$ arises, due to the adiabatic invariance of the ion magnetic moment ($p_{||,i}$ and $p_{\perp,i}$ are the ion pressures parallel and perpendicular to $\vec{B}$). When initially $\beta_i = 0.5$ ($\beta_i \equiv 8\pi p_i/|\vec{B}|^2$, where $p_i$ is the ion isotropic pressure), the pressure anisotropy is limited mainly by inelastic pitch-angle scattering provided by the IC instability, which in turn produces a non-thermal tail in the ion energy spectrum. After $\vec{B}$ is amplified by a factor $\sim 2.7$, this tail can be approximated as a power-law of index $\sim 3.4$ plus two non-thermal bumps, and accounts for $2-3\%$ of the ions and $\sim 18\%$ of their kinetic energy. On the contrary, when initially $\beta_i =2$, the ion scattering is dominated by the mirror instability and the acceleration is suppressed. This implies that efficient ion acceleration requires that initially $\beta_i \lesssim 1$. Although we focus on cases where $\vec{B}$ is amplified by plasma shear, we check that the acceleration occurs similarly if $\vec{B}$ grows due to plasma compression. Our results are valid in a sub-relativistic regime where the ion thermal energy is $\sim 10\%$ of the ion rest mass energy. This acceleration process can thus be relevant in the inner region of low-luminosity accretion flows around black holes

A Heating Mechanism via Magnetic Pumping in the Intracluster Medium

Turbulence driven by AGN activity, cluster mergers and galaxy motion constitutes an attractive energy source for heating the intracluster medium (ICM). How this energy dissipates into the ICM plasma remains unclear, given its low collisionality and high magnetization (precluding viscous heating by Coulomb processes). Kunz et al. 2011 proposed a viable heating mechanism based on the anisotropy of the plasma pressure (gyroviscous heating) under ICM conditions. The present paper builds upon that work and shows that particles can be gyroviscously heated by large-scale turbulent fluctuations via magnetic pumping. We study how the anisotropy evolves under a range of forcing frequencies, what waves and instabilities are generated and demonstrate that the particle distribution function acquires a high energy tail. For this, we perform particle-in-cell simulations where we periodically vary the mean magnetic field $\textbf{B}(t)$. When $\textbf{B}(t)$ grows (dwindles), a pressure anisotropy $P_{\perp}>P_{\parallel}$ ($P_{\perp}< P_{\parallel}$) builds up ($P_{\perp}$ and $P_{\parallel}$ are, respectively, the pressures perpendicular and parallel to $\textbf{B}(t)$). These pressure anisotropies excite mirror ($P_{\perp}>P_{\parallel}$) and oblique firehose ($P_{\parallel}>P_{\perp}$) instabilities, which trap and scatter the particles, limiting the anisotropy and providing a channel to heat the plasma. The efficiency of this mechanism depends on the frequency of the large-scale turbulent fluctuations and the efficiency of the scattering the instabilities provide in their nonlinear stage. We provide a simplified analytical heating model that captures the phenomenology involved. Our results show that this process can be relevant in dissipating and distributing turbulent energy at kinetic scales in the ICM.Comment: 24 pages, 17 figures, submitted to Ap

Chemical characterization of odorous emissions: A comparative performance study of different sampling methods

A comparison among different sampling methods (3 types of sorbent tubes and polymeric bags) commonly adopted in chemical analyses of odorous emissions was performed. To investigate the different performances, a lignocellulosic biomass storage plant was selected to obtain preliminary information about the chemical nature of odorous emissions. Samples of odorous emissions were collected at different biomass piles and analysed by dynamic olfactometry and TD-GC-MS. By comparing the two adopted sampling methods (tubes and bags), different performances are shown, depending on their specificity. By the comparison among the three types of sorbent tubes (Multi-sorbent bed (Carbotrap, Carbopack X and Carboxen 569), Tenax and Sulphur), Sulphur and Multi-sorbent bed present similar performance, while Tenax TA tubes show a different trend in terms of type and numerosity of detected compounds. In addition, from the comparison between tubes and polymeric bags, the number and types of compounds detected in bags are more comparable to those observed in the Multi-sorbent bed and Sulphur tubes. However, a difference between the two methods appears, especially in the detection of low-molecular weight organic compounds. In this study, it is possible to highlight that, due to the complexity of odorous emissions, the selection of the sampling material may affect the obtained chemical results. The detection of different classes of compounds, is a crucial point, to obtaining the most complete characterization of mixtures and comparing the chemical profile with olfactometric results: care must be taken in the choice of sampling material and procedure.Peer ReviewedPostprint (author's final draft

Bleaching melanin in formalin-fixed and paraffin-embedded melanoma specimens using visible light: a pilot study

In fluorescence microscopy, light radiation can be used to bleach fluorescent molecules in formalin-fixed and paraffin-embedded (FFPE) samples, in order to increase the ratio between signal of interest and background autofluorescence. We tested if the same principle can be exploited in bright field microscopy to bleach pigmented melanoma FFPE sections together with cell morphology maintenance. After dewaxing and rehydration, serial FFPE sections of a feline diffuse iris melanoma, a canine dermal melanoma, a gray horse dermal melanoma and a swine cutaneous melanoma were irradiated with visible light for I, 2, 3, 4 and 5 days, prior to Hematoxylin &amp; Eosin staining. Complete bleaching was obtained after 1-day treatment in feline and swine melanomas, while 2 and 3 days were required in canine and equine neoplasms, respectively. In all treated samples, cell morphology was maintained. Photo-induced bleaching combined with immunohistochemistry was tested after a 3-day photo-treatment using five different markers. According to the literature, in all samples neoplastic cells stained positive for vimentin, S100 and PNL2, while negative for FVIII and pancytokeratin. in conclusion, visible light can be effectively exploited to bleach pigmented melanoma FFPE sections prior to perform routine histochemical and immunohistochemical stains

Sulphur compounds: comparison of different sorbent tubes for their detection

Different techniques have been developed for the analysis of gaseous sulphur pollutants, to maximize the analytical signals. In a complex matrix, such as odorous emissions, the detection of sulphur compounds can be critical in GC analysis, due to the lower concentration of these pollutants and the disturbing effect of co-eluting hydrocarbons. However, their detection is fundamental because they have a non-negligible odour impact. In the field of gaseous emissions analytics, it is common to use sorbent tubes for the sampling step. This technology uses different adsorbent materials, with different selectivity depending on the nature of the gas to be analysed. This work aims to evaluate the ability of three different sorbent tubes to collect different sulphur compounds, belonging to the classes of mercaptans, thioethers and aromatic heterocyclic compounds. A standard solution of 10 sulphur compounds was prepared by diluting in methanol 50 µL of each liquid standard into a 10 mL flask. Subsequently, this solution was diluted in methanol to obtain sulphur standards at five different concentrations (approximately 5-500 ng/µL). The tubes were loaded with the standard solutions with an aliquot of each solution, using a gas chromatograph packed column injector and subsequently analysed by TD-GC-MS. By the results obtained - average Response Factor (RF) and its Relative Standard Deviation (% RSD), it is possible to conduct a comparison among these tubes and evaluate their performance. From the comparison of the tubes, discussing % RSD, it is possible to highlight a slightly better performance, in terms of the number of compounds with % RSD = 30%, for tubes specific for sulphur compounds. Focusing on RF values, multi-sorbent bed tubes show slightly higher RFs for very volatile sulphur compounds, but Sulphur tubes present higher RF values for 6 compounds out of 10 compounds considered. The performance of Tenax TA tubes, instead, appears strictly correlated with the compound’s volatility and therefore they don’t appear useful for sorption of very volatile compounds.Peer ReviewedPostprint (published version