Low Halo Research Articles

Reversing Arrested Development: A New Method to Address Halo Assembly Bias

Abstract Halo assembly bias is a phenomenon whereby the clustering of dark matter halos is dependent on halo properties, such as age, at fixed mass. Understanding the origin of assembly bias is important for interpreting the clustering of galaxies and constraining cosmological models. One proposed explanation for the origin of assembly bias is the truncation of mass accretion in low-mass halos in the presence of more massive halos, called ‘arrested development.’ Halos undergoing arrested development would have older measured ages and exhibit stronger clustering than equal mass halos that have not undergone arrested development. We propose a new method to test the validity of this explanation for assembly bias, and correct for it in cosmological N-body simulations. The method is based on the idea that the early mass accretion history of a halo, before arrested development takes effect, can be used to predict the late-time evolution of the halo in the absence of arrested development. We implement this idea by fitting a model to the early portion of halo accretion histories and extrapolating to late times. We then calculate ‘corrected’ masses and ages for halos based on this extrapolation and investigate how this impacts the assembly bias signal. We find that correcting for arrested development this way leads to a factor of two reduction in the strength of the assembly bias signal across a range of low halo masses. This result provides new evidence that arrested development is a cause of assembly bias and validates our approach to mitigating the effect.

The Local Bubble Is a Local Chimney: A New Model from 3D Dust Mapping

Leveraging a high-resolution 3D dust map of the solar neighborhood from Edenhofer et al., we derive a new 3D model for the dust-traced surface of the Local Bubble, the supernova-driven cavity surrounding the Sun. We find that the surface of the Local Bubble is highly irregular in shape, with its peak extinction surface falling at an average distance of 170 pc from the Sun (spanning 70–600+ pc) with a typical thickness of 35 pc and a total dust-traced mass of (6.0 ± 0.7) × 105 M ⊙. The Local Bubble displays an extension in the Galactic northern hemisphere that is morphologically consistent with representing a “local chimney.” We argue this chimney was likely created by the “bursting” of this supernova-driven superbubble, leading to the funneling of interstellar medium (ISM) ejecta into the lower Galactic halo. We find that many well-known dust features and molecular clouds fall on the surface of the Local Bubble and that several tunnels to other adjacent cavities in the ISM may be present. Our new, parsec-resolution view of the Local Bubble may be used to inform future analysis of the evolution of nearby gas and young stars, the investigation of direct links between the solar neighborhood and the Milky Way’s lower halo, and numerous other applications.

Composition, thermal, and microstructural characteristics of mutton tallows in comparison with beef tallows

AbstractThe composition, thermal properties, and microstructure of some mutton tallows (MTs), such as sheep tallow (ST), goat tallow (GT), and sheep tail tallow (STT), were investigated and compared with those of beef tallow (BT). The results showed that the fatty acids (FAs) in the MTs were dominated by oleic, stearic, and palmitic acids, which were similar to those of BTs; also there were some natural trans and odd‐carbon FAs occurred in these tallows. Comparison with STs, GTs, and BTs, STT had higher triunsaturated and diunsaturated‐monosaturated triacylglycerols (TAGs) and lower monounsaturated‐disaturated and trisaturated TAGs. Solid fat content (SFC) profile of STT was different those of STs, GTs, and BTs, whereas STs, GTs, and BTs had similar SFC profiles. In the range of 0–50°C, STT had a lower SFC compared with STs, GTs, and BTs at a given temperature. DSC results showed that MTs had melting and crystallization curves similar to BTs; and the GT, ST, and BT had higher melting and crystallization temperatures than STT. All MT and BTs crystals are β′ form; there also exists certain β form. The microscopic morphology of the STT was radial spherical aggregates, and those of other MT and BTs were consisted of radial inner core and low density outer halo area.Practical Application: The results of SFC, microstructure, and morphology indicated mutton tallows containing the desired crystal form and crystal morphology could be used as shortening base fats. The research can provide a theoretical basis for expanding the application of mutton tallows in food industry.

The baryon cycle in modern cosmological hydrodynamical simulations

ABSTRACT In recent years, cosmological hydrodynamical simulations have proven their utility as key interpretative tools in the study of galaxy formation and evolution. In this work, we present a comparative analysis of the baryon cycle in three publicly available, leading cosmological simulation suites: EAGLE, IllustrisTNG, and SIMBA. While these simulations broadly agree in terms of their predictions for the stellar mass content and star formation rates of galaxies at $z\approx 0$, they achieve this result for markedly different reasons. In EAGLE and SIMBA, we demonstrate that at low halo masses ($M_{\rm 200c}\lesssim 10^{11.5}\, \mathrm{M}_{\odot }$), stellar feedback (SF)-driven outflows can reach far beyond the scale of the halo, extending up to $2\!-\!3\times R_{\rm 200c}$. In contrast, in TNG, SF-driven outflows, while stronger at the scale of the interstellar medium, recycle within the circumgalactic medium (within $R_{\rm 200c}$). We find that active galactic nucleus (AGN)-driven outflows in SIMBA are notably potent, reaching several times $R_{\rm 200c}$ even at halo masses up to $M_{\rm 200c}\approx 10^{13.5}\, \mathrm{M}_{\odot }$. In both TNG and EAGLE, AGN feedback can eject gas beyond $R_{\rm 200c}$ at this mass scale, but seldom beyond $2\!-\!3\times R_{\rm 200c}$. We find that the scale of feedback-driven outflows can be directly linked with the prevention of cosmological inflow, as well as the total baryon fraction of haloes within $R_{\rm 200c}$. This work lays the foundation to develop targeted observational tests that can discriminate between feedback scenarios, and inform subgrid feedback models in the next generation of simulations.

EDIG-CHANGES. II. Project Design and Initial Results on NGC 3556

The extraplanar diffuse ionized gas (eDIG) represents ionized gases traced by optical/UV lines beyond the stellar extent of galaxies. We herein introduce a novel multislit narrow-band spectroscopy method to conduct spatially resolved spectroscopy of the eDIG around a sample of nearby edge-on disk galaxies (eDIG-CHANGES). In this paper, we introduce the project design and major scientific goals, as well as a pilot study of NGC 3556 (M108). The eDIG is detected to a vertical extent of a few kiloparsecs above the disk, comparable to the X-ray and radio images. We do not see significant vertical variation of the [N ii]/Hα line ratio. A rough examination of the pressure balance between different circumgalactic medium phases indicates the magnetic field is in a rough pressure balance with the X-ray emitting hot gas and may play an important role in the global motion of both the eDIG and the hot gas in the lower halo. At the location of an Hubble Space Telescope/Cosmic Origins Spectrograph observed UV bright background active galactic nucleus ∼29 kpc from the center of NGC 3556, the magnetic pressure is much lower than that of the hot gas and the ionized gas traced by UV absorption lines, although the extrapolation of the pressure profiles may cause some biases in this comparison. By comparing the position–velocity diagrams of the optical and CO lines, we also find the dynamics of the two gas phases are consistent with each other, with no evidence of a global inflow/outflow and a maximum rotation velocity of ∼150 km s−1.

On the origin of globular clusters in a hierarchical universe

ABSTRACT We present an end-to-end description of the formation of globular clusters (GCs) combining a treatment for their formation and dynamical evolution within galaxy haloes with a state-of-the-art semi-analytic simulation of galaxy formation. Our approach allows us to obtain exquisite statistics to study the effect of the environment and assembly history of galaxies, while still allowing a very efficient exploration of the parameter space. Our reference model, including both efficient cluster disruption during galaxy mergers and dynamical friction of GCs within the galactic potential, accurately reproduces the observed correlation between the total mass in GCs and the parent halo mass. A deviation from linearity is predicted at low-halo masses, which is driven by a strong dependence on morphological type: bulge-dominated galaxies tend to host larger masses of GCs than their later-type counterparts. While the significance of the difference might be affected by resolution at the lowest halo masses considered, this is a robust prediction of our model and a natural consequence of the assumption that cluster migration into the halo is triggered by galaxy mergers. Our model requires an environmental dependence of GC radii to reproduce the observed low-mass mass distribution of GCs in our Galaxy. At GC masses $\gt 10^6\, {\rm M}_\odot$, our model predicts fewer GCs than observed, due to an overly aggressive treatment of dynamical friction. Our model reproduces well the metallicity distribution measured for Galactic GCs, even though we predict systematically younger GCs than observed. We argue that this adds further evidence for an anomalously early formation of the stars in our Galaxy.

DA-DRN: A degradation-aware deep Retinex network for low-light image enhancement

This paper proposes a Degradation-Aware Deep Retinex Network (DA-DRN) for enhancing low-light images. DA-DRN is composed of a decomposition U-Net and an enhancement U-Net, and can tackle various degradation issues commonly found in real-world low-light environments, such as low brightness, color distortion, unknown noise, invisible detail, and halo artifacts. To achieve noise removal while preserving details, we introduce a Degradation-Aware Module (DA Module) that guides the decomposer's training process and enables it to be a restorer during training without additional computational cost in the test phase. The DA Module also addresses color distortion and halo artifacts. To train the enhancement network, we use Perceptual Loss to generate brightness-improved illumination maps that are more consistent with human visual perception. Our proposed model is trained and evaluated on the popular LOL real-world and synthetic datasets, as well as several other frequently used datasets without Ground-Truth (LIME, DICM, MEF, and NPE datasets). The results demonstrate that our method achieves promising performance with good robustness and generalization, outperforming many other state-of-the-art methods both qualitatively and quantitatively. Additionally, our method only takes 7 ms to process an image with 600×400 resolution on a TITAN Xp GPU.

On the anticorrelation between pericentric distance and inner dark matter density of Milky Way’s dwarf spheroidal galaxies

ABSTRACT An anticorrelation between the central density of the dark matter (DM) halo (ρ150, DM) and the pericentric distances (rp) of the Milky Way’s (MW’s) dwarf spheroidal galaxies (dSphs) has been reported in the literature. The existence and origin of such anticorrelation are, however, controversial, one possibility being that only the densest dSphs can survive the tidal field towards the centre of our Galaxy. In this work, we place particular emphasis on quantifying the statistical significance of such anticorrelation, by using available literature data in order to explore its robustness under different assumptions on the MW gravitational potential, and for various derivations of ρ150 and rp. We consider models in which the MW is isolated and has low ($8.8\times 10^{11}\, {\rm M}_{\odot }$ ) and high ($1.6\times 10^{12}\, {\rm M}_{\odot }$ ) halo masses, respectively, as well as configurations in which the MW’s potential is perturbed by a Large Magellanic Cloud (LMC) infall. We find that, while data generally support models in which the dSphs’ central DM density decreases as a function of their pericentric radius, this anticorrelation is statistically significant at 3σ level only in ${\sim} 12~{{ \rm per\ cent}}$ of the combinations of ρ150 and rp explored. Moreover, including the impact of the LMC’s infall on to the MW weakens or even washes away this anticorrelation, with respect to models in which the MW is isolated. Our results suggest that the strength and existence of such anticorrelation are still debatable: exploring it with high-resolution simulations including baryonic physics and different DM flavours will help us to understand its emergence.

Quantum tunneling of ultralight dark matter out of satellite galaxies

The idea of ultralight scalar (axion) dark matter is theoretically appealing and may resolve some small-scale problems of cold dark matter; so it deserves careful attention. In this work we carefully analyze tunneling of the scalar field in dwarf satellites due to the tidal gravitational force from the host halo. The tidal force is far from spherically symmetric; causing tunneling along the axis from the halo center to the dwarf, while confining in the orthogonal plane. We decompose the wave function into a spherical term plus higher harmonics, integrate out angles, and then numerically solve a residual radial Schrödinger-Poisson system. By demanding that the core of the Fornax dwarf halo can survive for at least the age of the universe places a bound on the dark matter particle mass 2 × 10-22 eV ≲ m ≲ 6 × 10-22eV. Interestingly, we show that if another very low density halo is seen, then it rules out the ultralight scalar as core proposal completely. Furthermore, the non-condensed particles likely impose an even sharper lower bound. We also determine how the residual satellites could be distributed as a function of radius.

On the Origin of the North Celestial Pole Loop

The North Celestial Pole Loop (NCPL) provides a unique laboratory for studying the early-stage precursors of star formation. Uncovering its origin is key to understanding the dynamical mechanisms that control the evolution of its contents. In this study, we explore the 3D geometry and the dynamics of the NCPL using high-resolution dust extinction data and H i data, respectively. We find that material toward Polaris and Ursa Major is distributed along a plane similarly oriented to the Radcliffe wave. The Spider projected in between appears disconnected in 3D, a discontinuity in the loop shape. We find that the elongated cavity that forms the inner part of the NCPL is a protrusion of the Local Bubble (LB) likely filled with warm (possibly hot) gas that passes through and goes beyond the location of the dense clouds. An idealized model of the cavity as a prolate spheroid oriented toward the observer, reminiscent of the cylindrical model proposed by Meyerdierks et al., encompasses the protrusion and fits into arcs of warm H i gas expanding laterally to it. As first argued by Meyerdierks et al., the nonspherical geometry of the cavity and the lack of OB stars interior to it disfavor an origin caused by a single point-like source of energy or multiple supernovae. Rather, the formation of the protrusion could be related to the propagation of warm gas from the LB into a pre-existing nonuniform medium in the lower halo, the topology of which was likely shaped by past star formation activity along the Local Arm.

Preoperative prediction of macrotrabecular-massive hepatocellular carcinoma based on B-Mode US and CEUS.

To develop a preoperative prediction model to identify macrotrabecular-massive hepatocellular carcinoma (MTM-HCC) and evaluate the model's diagnostic performance in differentiating MTM-HCC from HCC. We conducted a mono-center retrospective study in a grade A tertiary hospital in China. Consecutive patients with suspected HCC from February 2019 to December 2020 were eligible for inclusion. All consenting patients underwent CEUS examination and were histologically diagnosed. Based on the clinical and US features between the two groups, we developed a binary logistic regression model and a nomogram for predicting MTM-HCC. A total of 161 patients (median age, 57 years; interquartile range, 48-64 years; 129 men) were included in the analysis. Twenty-seven of the HCCs (16.8%) were of the MTM subtype. Binary logistic regression analysis indicated that PVP hypoenhancement (OR = 15.497; 95% CI: 1.369, 175.451; p = 0.027), AFP > 454.6 ng/mL (OR = 8.658; 95% CI: 3.030, 24.741; p < 0.001), ALB ≤ 29.9 g/L (OR = 3.937; 95% CI: 1.017, 15.234; p = 0.047), halo sign (OR = 3.868; 95% CI: 1.314, 11.391; p = 0.016), and intratumoral artery (OR = 2.928; 95% CI: 1.039, 8.255; p = 0.042) were predictors for MTM subtype. Combining any two criteria showed a high sensitivity (100.0%); combining all five criteria showed a high specificity (99.2%); and the AUC value of the logistic regression model was 0.88 (95% CI: 0.81, 0.92). BMUS and CEUS could be used for identifying patients suspected of having MTM-HCC. Combining clinical information, BMUS, and CEUS features could achieve a noninvasive diagnosis of MTM-HCC. • Contrast-enhanced ultrasound examination helps clinicians to identify MTM-HCCs preoperatively. • PVP hypoenhancement, high AFP levels, low ALB levels, halo signs, and intratumoral arteries could be used to predict MTM-HCCs. • A logistic regression model and nomogram were built to noninvasively diagnose MTM-HCCs with an AUC value of 0.88 (95% CI: 0.81, 0.92).

Utilize empirical models of measured relative dose output factor (rDOF) and transverse penumbra (TP) to evaluate dosimetric uncertainties of in-air spot modelling for spot-scanning carbon-ion and proton radiotherapy

ABSTRACT To evaluate the dosimetric uncertainties of symmetric Gaussian modelled in-air spot size/shape in our Syngo treatment planning system, we performed measurements of rDOF and TP width at a shadow depth of 2.7 mm. They are related to the effects of low dose halo and asymmetric spot shape. Empirically, a two-component Gaussian analytical model predicted the trend of rDOF and TP as a function of field size. From the result, the in-air spot size was described by a single Gaussian function for carbon-ion and high energy proton. The weights and widths for the second component of double Gaussian increased significantly as the beam energy decreases for protons. The TP fitting agreed with the rDOF fit for the scanned field (SF) of larger than 78 mm. For proton, the TP for SF of 12.0 mm for energies of 153.36 MeV/u and197.23 MeV/u, SF of 60.0 mm for energy of 48.08 MeV/u were fit better by single Gaussian component. The width of TP showed no field size dependence for each energy. Obtained Gaussian width by fitting TP was smaller than by fitting rDOF for carbon-ion. The empirical model allowed us to investigate the effects of beam emittance and scattering. They could provide reference values for clinical use and quality assurance.

Dipolar dark matter simulations on galaxy scales with the ramses code

Abstract We numerically explore on galaxy scales the dipolar dark matter (DM) model based on the concept of gravitational polarization. This DM model has been proposed as a natural way to reproduce observed tight galactic scaling relations such as the baryonic Tully–Fisher relation and the Radial Acceleration Relation. We present a customized version of the RAMSES code including for the first time the dynamics of this Dipolar DM in N-body simulations. As a first application of this code, we check that we recover an equilibrium configuration that had been found analytically, where a low density Dipolar DM halo is at rest with respect to its central galaxy, recovering the aforementioned scaling relations. A characteristic signature of this equilibrium model is that it harbours a dynamical instability with a characteristic time depending on the Dipolar DM halo density, which we recover numerically. This represents a first step towards more involved simulations needed to test this framework, ranging from galaxy interactions to structure formation.

Understanding the ‘feeble giant’ Crater II with tidally stretched wave dark matter

ABSTRACT The unusually large ‘dwarf’ galaxy Crater II, with its small velocity dispersion, ≃3 km s−1, defies expectations that low-mass galaxies should be small and dense. We combine the latest stellar and velocity dispersion profiles finding Crater II has a prominent dark core of radius $\simeq 0.71^{+0.09}_{-0.08}$ kpc, surrounded by a low density halo, with a transition visible between the core and the halo. We show that this profile matches the distinctive core-halo profile predicted by ‘Wave Dark Matter’ as a Bose-Einstein condensate, ψDM, where the ground state soliton core is surrounded by a tenuous halo of interfering waves, with a marked density transition predicted between the core and halo. Similar core-halo structure is seen in most dwarf spheroidal galaxies (dSphs), but with smaller cores, ≃0.25 kpc and higher velocity dispersions, ≃9 km s−1, and we argue here that Crater II may have been a typical dSph that has lost most of its halo mass to tidal stripping, so its velocity dispersion is lower by a factor of 3 and the soliton is wider by a factor of 3, following the inverse scaling required by the Uncertainty Principle. This tidal solution for Crater II in the context of ψDM is supported by its small pericenter of ≃20 kpc established by Gaia, implying significant tidal stripping of Crater II by the Milky Way is expected.

A novel IoT sensor authentication using HaLo extraction method and memory chip variability

Since the inception of encrypted messages thousands of years ago, mathematicians and scientists have continued to improve encryption algorithms in order to create more secure means of communication. These improvements came by means of more complex encryption algorithms that have stronger security features such as larger keys and trusted third parties. While many new processors can handle these more complex encryption algorithms, IoT devices on the edge often struggle to keep up with resource intensive encryption standards. In order to meet this demand for lightweight, secure encryption on the edge, this paper proposes a novel solution, called the High and Low (HaLo) method, that generates Physical Unclonable Function (PUF) signatures based on process variations within flash memory. These PUF signatures can be used to uniquely identify and authenticate remote sensors, and help ensure that messages being sent from remote sensors are encrypted adequately without requiring computationally expensive methods. The HaLo method consumes 20x less power than conventional authentication schemes commonly used with IoT devices, it has an average latency of only 39ms for 512 bit signature generation, and the average error rate is below 0.06%. Due to its low latency, low error rate, and high power efficiency, the HaLo method can progress the field of IoT encryption standards by accurately and efficiently authenticating remote sensors without sacrificing encryption integrity.

Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies

ABSTRACT Recent progress of nucleosynthesis work as well as the discovery of a kilonova associated with the gravitational-wave source GW170817 indicates that neutron star mergers (NSM) can be a site of the r-process. Several studies of galactic chemical evolution, however, have pointed out inconsistencies between this idea and the observed stellar abundance signatures in the Milky Way: (a) the presence of Eu at low (halo) metallicity and (b) the descending trend of Eu/Fe at high (disc) metallicity. In this study, we explore the galactic chemical evolution of the Milky Way’s halo, disc, and satellite dwarf galaxies. Particular attention is payed to the forms of delay-time distributions for both type Ia supernovae (SN Ia) and NSMs. The Galactic halo is modelled as an ensemble of independently evolving building-block galaxies with different masses. The single building blocks as well as the disc and satellite dwarfs are treated as well-mixed one-zone systems. Our results indicate that the aforementioned inconsistencies can be resolved and thus NSMs can be the unique r-process site in the Milky Way, provided that the delay-time distributions satisfy the following conditions: (i) a long delay (∼1 Gyr) for the appearance of the first SN Ia (or a slow early increase of its number) and (ii) an additional early component providing ${\gtrsim}50{{\ \rm per\ cent}}$ of all NSMs with a delay of ∼0.1 Gyr. In our model, r-process-enhanced and r-process-deficient stars in the halo appear to have originated from ultrafaint dwarf-sized and massive building blocks, respectively. Our results also imply that the natal kicks of binary neutron stars have a little impact on the evolution of Eu in the disc.

Analysis of Development Mechanism of Giant Cell Arteritis in Nude Mouse Model through Color Duplex Sonography and Computerized Tomography Nanocontrast Agent.

To explore the application value of color duplex sonography and enhanced computerized tomography (CT) inspection based on a nanocontrast agent in diagnosis and pathogenesis in giant cell arteritis (GCA), the GCA nude mouse model was constructed. In this study, 40 healthy male BalB/c nude mice aged 6-8 weeks were randomly divided into a control group (no model) and an experimental group (model), with 20 mice in each group, and the temporal artery tissue of GCA patients diagnosed as positive by temporal artery biopsy was implanted into nude mice to construct a GCA nude mouse model. Abdominal aortic biopsy and immunohistochemistry were used to verify the success of the GCA nude mouse model. All nude mice were subjected to color duplex sonography and enhanced CT examination based on a nanocontrast agent. At the same time, the basic indicators such as body weight, temperature, white blood cell (WBC), lymphocytes (LYM), hemoglobin (HGB), and platelet (PLT) were measured, and the protein expression levels of interleukin-6 (IL-6) and signal transducer and activator of transcription 3 (STAT3) were detected by immunohistochemistry. The results showed that the temporal artery wall of the nude mice in the experimental group thickened and the lumen was significantly narrowed, indicating that the cell arteritis model of nude mice was successfully constructed; ultrasound examination showed that the right superficial temporal artery vascular cavity narrowed, the blood flow signal changed like a filling defect around the periphery, and there was a low echo halo. CT examination showed that the left superficial temporal artery narrowed, and the inner diameter of the narrow segment of blood vessels changed like a bead. The body weight of nude mice in the experimental group decreased significantly after the modeling was completed (P < 0.05); after modeling, the body temperature of the nude mice in the experimental group increased significantly (P < 0.05); LYM and HGB values of nude mice in the experimental group were significantly lower than those in the control group (P < 0.05); the content of IL-6, STAT3, IL-6, and STAT3 proteins in the arterial tissue of nude mice in the experimental group was lower than that of the control group (P < 0.05), indicating that color duplex sonography and CT contrast agent technology can be used in the diagnosis and development mechanism research of GC.

Multitracer Cosmological Line Intensity Mapping Mock Light-cone Simulation

Abstract Submillimeter emission lines are important tracers of the cold gas and ionized environments of galaxies and the targets for future line intensity mapping surveys. Physics-based simulations that predict multiple emission lines arising from different phases of the interstellar medium are crucial for constraining the global physical conditions of galaxies with upcoming line intensity mapping observations. In this work, we present a general framework for creating multitracer mock submillimeter line intensity maps based on physically grounded galaxy formation and submillimeter line emission models. We simulate a mock light cone of 2 deg2 over a redshift range 0 ≤ z ≤ 10 comprising discrete galaxies and galaxy [C ii], CO, and [C i] emission. We present simulated line intensity maps for two fiducial surveys with resolution and observational frequency windows representative of COMAP and EXCLAIM. We show that the star formation rate and line emission scaling relations predicted by our simulation significantly differ at low halo masses from widely used empirical relations, which are often calibrated to observations of luminous galaxies at lower redshifts. We show that these differences lead to significant changes in key summary statistics used in intensity mapping, such as the one-point intensity probability density function and the power spectrum. It will be critical to use more realistic and complex models to forecast the ability of future line intensity mapping surveys to measure observables such as the cosmic star formation rate density.

Spectral analysis of χ class data of GRS 1915+105 using TCAF solution

The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Comptonization Efficiency (CE), which is the ratio of power-law and blackbody photons. However, CE estimation is based on an empirical model which does not provide us with a comprehensive picture regarding accretion flow dynamics around the central source. In reality, the accretion flow is comprised of two components: the high angular momentumKeplerian flow in the form of a radiatively efficient disk and a low angular momentumradiatively inefficient sub-Keplerian halo enveloping the disk. These two components contribute differently to the overall flux due to the differences in their radiative efficiencies. Therefore, it is necessary to analyze the spectral behaviors and time variabilities in terms of accretion rates. In χ class, X-ray flux is steady with no significant variation, however various χ subclasses are observed at different X-ray fluxes and variations of count rates across different χ subclasses must be linked to the variation of flow parameters such as the accretion rates, be it the Keplerian disk rate and/or the low angular momentum halo rate. This motivated us to analyze the spectra of the χ class data implementing the physical Two Component Advective Flow (TCAF) solution which directly extracts these two rates from spectral fits. We find that in the χ 2,4 classes, which are reportedly devoid of significant outflows, the spectra could be fitted well applying the TCAF solution alone. In the χ 1,3 classes, which are always linked with outflows, a cutoff power-law model is needed in addition to the TCAF solution. At the same time, the normalization required by this model along with the variation of photon index and exponential roll-off factor provides us with information on the relative dominance of the outflow in the latter two classes. TCAF fit also supplies us with the size and location of the Compton cloud along with its optical depth. Thus by fitting with TCAF, a physical understanding of the flow geometry in different χ classes of GRS 1915+105 has been obtained.

Investigation of Ambipolar Conduction and RF Stability Performance in Novel Germanium Source Dual Halo Dual Dielectric Triple Material Surrounding Gate TFET

In this study, we present an ambipolar conduction and RF stability performance for a Germanium Source Dual Halo Dual Dielectric Triple Material Surrounding Gate Tunnel FET (Ge(SRC)-DH-DD-TM-SG-TFET). The energy band diagram of the device will be derived using the Stern Stability Factor. The minimum tunneling length is expressed using low-k Silicon dioxide (SiO2) and high-k Hafnium oxide (HfO2) as dual dielectric material. Then the band to band tunneling (BTBT) rate tunneling generation rate will be derived using Kane’s model. In terms of frequency efficiency the proposed device with SiO2/HfO2 as gate dielectric is good enough to attain high cut-off frequency (fT) of 94.22 GHz is observed at drain to source voltage of VDS = 1 V. Efforts have also been made to properly assess the potential of the two halo doped regions regions. An expression for transconductance is proposed and the model is validated using 3-D Silvaco Atlas TCAD device simulator. In addition, to demonstrate the advantage of using Ge(SRC)-DH-DD-TM-SG-TFET dual dielectric halo doping in circuit applications, the transient response of the conventional TFET germanium source is compared with the low and high-k dielectric halo doping Ge(SRC) TFET.