Point Of Maximum Density Research Articles

Experimental study on mechanical and acoustic emission characteristics of red sandstone containing combined flaws of hole-fissure under biaxial compression

To investigate the mechanical behaviour and failure mechanism of flawed rock masses under biaxial stress conditions, a series of biaxial compression experiments are conducted on red sandstone specimens containing combined flaws of the circular hole and perforated symmetric fissure combined with acoustic emission (AE) technology in this work. The results show a close association between the stress-strain curve morphology and confining stress, both the biaxial compression strength and elastic modulus exhibit an upward trend with increasing fissure angle and confining stress. The maximum AE energy and cumulative AE energy both increase with higher confining stress. The crack types in the specimens are identified by analyzing the AF/RA value distribution, revealing a gradual decrease in the percentage of tensile cracks with increasing fissure angle. An AE localization algorithm based on the least absolute value method is applied to pinpoint AE events during biaxial compression, and AE events distribution is analyzed through the Kernel density estimation (KDE). The crack extension behaviour is described based on the movement of the maximum kernel density points, which initially exhibits a progression from both ends of the specimen towards the central region and subsequently from the central fissure tip towards the two ends.

Three-Dimensional Density And Flight Direction Measurement In The Ballistic Range

Simultaneous measurement of the three-dimensional density field around the Hayabusa-type re-entry capsule model and the angle of attack using the 3D-BOS (Background Oriented Schlieren) technique was carried out in the ballistic range at the Institute of Fluid Science (IFS), Tohoku University. A Hayabusa-type re-entry capsule model with a diameter of 25 mm was used for the test model, and the free-flight Mach number was 1.20. A total of 22 digital cameras were installed for the two set of 3D-BOS measurement system. Each of 11 digital cameras are synchronized and captures the flow field around the test model at two different moments. In this paper, the model position at the different moments were measured using two sets of 3D-BOS measuring systems based on image processing, and the model flight direction and angle of attack were measured. The results showed that the stagnation point predicted from the angle of attack and the maximum density point showed good agreement. Therefore, we conclude that the density distribution around the reentry capsule model obtained by the 3D-BOS technique can be directly compared with the CFD results.

Energy evolution mechanism during rockburst development in structures of surrounding rocks of deep rockburst-prone roadways in coal mines

Influenced by the deep high-stress environment, geological structures, and mining disturbance in coal mines, the frequency of rockburst disasters in roadways is increasing. This research analyzed energy evolution characteristics during rockburst development in the elastic bearing zone and energy conversion in the plastic failure zone. The critical energy criteria for structural instability of roadway surrounding rocks were deduced. Numerical software was also applied to simulate the energy evolution during rockburst development in surrounding rocks of rockburst-prone roadways under conditions of different mining depths and coal pillar widths. The occurrence mechanism of rockburst deep in coal mines was analyzed from the perspective of energy in structures of deep roadway surrounding rock in coal mines. The research results show that the critical energy criteria are closely related to the elastic strain energy stored in deep roadway surrounding rocks and the energy absorbed by support systems. The impact energy in roadways is directly proportional to the square of the stress concentration factor k. Moreover, as the mining depth increases, the location of the peak point of maximum energy density gradually shifts to coal ahead of the working face. The larger the mining depth is, the more significantly the energy density is influenced by advanced abutment pressure of the working face and the wider the affected area is. With the increment of the coal pillar width, the distance from the peak point of energy density to the roadway boundary enlarges abruptly at first and then slowly, and the critical coal pillar width for gentle change in the distance is 30 m. Changes in the peak elastic energy density in coal pillars with the coal pillar width can be divided into four stages: the slow increase stage, abrupt increase stage, abrupt decrease stage, and slow decrease stage. The elastic energy density is distributed asymmetrically in deep roadway surrounding rocks in coal mines. Under the action of structures of roadway surrounding rocks, energy evolution in these structures differs greatly during rockburst development under conditions of different coal pillar widths. This research provides an important theoretical basis for the support of rockburst-prone roadways during deep coal mining.

Real Solar Cell and Determination Methods of Electrical Parameters

In this work, we develop methods to determine the characteristic electrical parameters of a photovoltaic cell such as the photocurrent density (Jph), the saturation current density (J0), the short-circuit current density (Jsc), the open-circuit voltage (Voc), the maximum power density point (Jm , Vm), the fill factor (FF) and the electrical conversion efficiency (etaC) according to the irradiance spectrum. The real solar cell model is considered for the determination of these various parameters. This model takes into account the effect of shunt and series resistances (parasitic resistances). Notions of semiconductor physics, continuity equation of charge carriers combined to optoelectronic and geometrical properties of the materials, numerical resolution method to solve implicit equations based on characteristic equation of a photodiode, are notions mainly exploited to determine electrical parameters of the real solar cell. The results are applied to the heterostructures ZnO(n+)/CdS(n)/CuInS2(p)/ CuInSe2(p+) named CIS and ZnO(n+)/CdS(n)/CuInSe2(p)/CuInS2(p+) named CISE to evaluate their performances according to the considered parameters. The results obtained for each structure, photocurrent density ~ 17 mA.cm-2 (CIS) and 31 mA.cm-2 (CISE), short-circuit current density ~ 16.79 - 17 mA.cm-2 (CIS) and 30.62 - 31 mA.cm-2 (CISE), open-circuit voltage ~ 0.76 V (CIS) and 0.52 V (CISE), fill factor ~ 0.648 - 0.745 (CIS) and 0.545 - 0.677 (CISE), maximum power density ~ 8.28 - 9.69 mW.cm-2 (CIS) and 8.72 - 11.02 mW.cm-2 (CISE), saturation current ~ 4.117×10-8 mA.cm-2 (CIS) and 1.169×10-3 mA.cm-2 (CISE), are in the same magnitude order as the values published in the literature. We obtain under AM 1.5 solar spectrum and taken into account the parasitic resistances, a theoretical conversion efficiency ranging from 9.93% to 11.62% for the model CIS and from 10.46% to 13.22% for the model CISE. Thus, these results allow to validate the various models established to model the phenomena studied.

Ideal Solar Cell Electrical Parameters and Ideality Factor Effect on the Efficiency

The determination of the electrical conversion efficiency (η<SUB>C</SUB>) is particularly important to evaluate the performance of a solar cell. For the evaluation of the efficiency by considering the ideal solar cell characterized by an absence of parasitic resistances and using the characteristic equation which corresponds to the equivalent electrical diagram, we determine the electrical parameters such as: the saturation current density (J₀), the short-circuit current density (J_sc), the open-circuit voltage (V_oc), the maximum power density point (J_m, V_m) and the fill factor (FF). The saturation current density is determined using fundamental semiconductor notions. The effect of the ideality factor on the electrical efficiency and the various parameters is also highlited. The results are applied to heterostructures based on CuInS₂ and CuInSe₂. The performance of the cell increases with a raising of the ideality factor (η) for the ideal solar cell model. By varying the ideality factor from 1 to 3, the calculated efficiency varies theoretically from 8.4% to 25.3% under AM1.5 solar spectrum for the structure based on CdS(n)/CuInS₂(p) named model (b) with a photocurrent density evaluated at 17 <i>mA.cm</i>^-2 by numerical calculation method. The efficiency varies from 6.8% to 20.45% for the structure based on CdS(n)/CuInSe₂(p) named model (a) with a photocurrent density evaluated at 31 <i>mA.cm</i>^-2 for the same used parameters. The open-circuit voltage varies from 0.5 V to 1.5 V for model (b) and from 0.27 V to 0.8 V for model (a). The results obtained (efficiency and electrical parameters) for each model remain within the range of experimental values published in the literature for solar cells based on chalcopyrite materials such as CIGS (CuIn_xGa_1-xSe₂ or CuIn_xGa_1-x(S_ySe_1-y)₂), and thus allowing to validate the different methods established to model the studied phenomena.

Experimental study on shear failure modes and acoustic emission characteristics of rock-like materials containing embedded 3D flaw

In nature, rock mass usually contains natural defects, which affect the mechanical properties of rock mass. At the same time, the failure of rock mass is often accompanied by shear failure behavior. Therefore, it is great significance to monitor and predict the shear failure process of fractured rock mass in order to ensure the stability of structure and the safety of construction. In this study, a method for making rock-like samples containing embedded 3D flaw is proposed and a series of shear tests are carried out under different normal stresses. The test results show that the complex shear stress-shear displacement curve can be divided into four stages. The shear strength, residual strength and shear modulus of the specimens are affected by the flaw dip angle and normal stress. The tensile failure mode is more likely to occur in low stress and small flaw angle specimens, while the shear failure mode mainly occurs in high stress specimens. A sudden increase in AE counts, AE event rates, and a sudden decrease in b-value to a minimum are usually precursors to rock failure. The RA/AF value can accurately reflect the classification and development of rock tension shear cracks. Through the Kernel density estimation (KDE) analysis on the distribution of AE events, the damage locations of rock-like in each stage are effectively identified. The movement of the maximum density point is consistent with the rock crack propagation tendency, almost following the uniform diffusion of the specimens from the middle to the end.

Mechanisms and effects of under-ice warming water in Ngoring Lake of Qinghai–Tibet Plateau

Abstract. The seasonal ice cover in lakes of the Qinghai–Tibet Plateau is a transient and vulnerable part of the cryosphere, whose characteristics depend on the regional climate: strong solar radiation in the context of the dry and cold environment because of the high altitude and relatively low latitude. We use the first under-ice temperature observations from the largest Tibetan freshwater lake, Ngoring Lake, and a one-dimensional lake model to quantify the mechanism of solar thermal accumulation under ice, which relies on the ice optical properties and weather conditions, as well as the effect of the accumulated heat on the land–atmosphere heat exchange after the ice breakup. The model was able to realistically simulate the feature of the Ngoring Lake thermal regime: the “summer-like” temperature stratification with temperatures exceeding the maximum density point of 3.98 ∘C across the bulk of the freshwater column. A series of sensitivity experiments revealed solar radiation was the major source of under-ice warming and demonstrated that the warming phenomenon was highly sensitive to the optical properties of ice. The heat accumulated under ice contributed to the heat release from the lake to the atmosphere for 1–2 months after ice-off, increasing the upward sensible and latent surface heat fluxes on average by ∼ 50 and ∼ 80 W m−2, respectively. Therefore, the delayed effect of heat release on the land–atmosphere interaction requires an adequate representation in regional climate modeling of the Qinghai–Tibet Plateau and other lake-rich alpine areas.

Exploring crystal structure by three-dimensional atomic density distribution from molecular dynamics simulations

Predicting crystal structure has been one of the core issues in materials research. X-ray diffraction data can generally be used to fit and refine the positions of atoms within the unit cell. However, for a system with part of its atoms diffusing or hopping below the melting temperature, the atoms inside the crystal begin to vibrate, diffuse, or hop when its temperature gradually rises. Even using the partial-occupancy concept, it becomes difficult or impossible to fit the structure due to the trial-and-error characteristic of refinement. More importantly, the limited partial-occupancy positions are insufficient and inappropriate to describe material systems containing diffusing or hopping atoms. To address this shortcoming, we proposed to perform molecular dynamics simulations and then add up all the positions of diffusing atoms in each time step to form a three-dimensional atomic density distribution into the primitive or conventional unit cell. The maximum atomic density points correspond to the partial-occupancy positions in x-ray diffraction data. The connected atomic density distribution identifies and defines the diffusing paths for mobile atoms within the crystal.

Experimental study on uniaxial compression failure modes and acoustic emission characteristics of fissured sandstone under water saturation

Widely distributed fissures in the open-pit slope (especially those which are in water-rich conditions) determine the slope stability. In order to study the effects of water and fissures on rock’s mechanical properties and corresponding acoustic emission characteristics, red sandstones containing dual-fissure with different angle configurations were prepared for uniaxial compression tests along with acoustic emission (AE) monitoring in this study. The impacts of water content and fissure angles on rock strength, failure mode and acoustic emission characteristics were analyzed. Moreover, the kernel density estimation (KDE) was accepted to quantify the AE events spatial distribution, then distinguishing difference between dry and saturated rocks’ failure modes. This study reveals that the presence of water in the rock lowers of the rock strength and decreases the amounts of secondary cracks and acoustic emission counts. As the fissure angle increases, both the rock strength and acoustic emission counts increase and the failure mode shifts from the tension failure to the shear failure. The b value was highly sensitive to crack propagation, reaching around 0.5 when the rock was finally destroyed under different water conditions. AE events mainly gathered in the location where the main cracks occurred. The maximum KDE density points of dry sandstone changed from concentrated state to dispersed state before failure, while the maximum density points of saturated sandstone always gathered in the middle of rock. The results of this paper lay theoretical foundations for monitoring and pre-warning of engineering rock failure in water environment.

Performance Analysis and Four-Objective Optimization of an Irreversible Rectangular Cycle.

Based on the established model of the irreversible rectangular cycle in the previous literature, in this paper, finite time thermodynamics theory is applied to analyze the performance characteristics of an irreversible rectangular cycle by firstly taking power density and effective power as the objective functions. Then, four performance indicators of the cycle, that is, the thermal efficiency, dimensionless power output, dimensionless effective power, and dimensionless power density, are optimized with the cycle expansion ratio as the optimization variable by applying the nondominated sorting genetic algorithm II (NSGA-II) and considering four-objective, three-objective, and two-objective optimization combinations. Finally, optimal results are selected through three decision-making methods. The results show that although the efficiency of the irreversible rectangular cycle under the maximum power density point is less than that at the maximum power output point, the cycle under the maximum power density point can acquire a smaller size parameter. The efficiency at the maximum effective power point is always larger than that at the maximum power output point. When multi-objective optimization is performed on dimensionless power output, dimensionless effective power, and dimensionless power density, the deviation index obtained from the technique for order preference by similarity to an ideal solution (TOPSIS) decision-making method is the smallest value, which means the result is the best.

Post-Operative Complications of Surgery for Chronic Subdural Hematoma (SDH) and Prevention

Objective: The study aimed to determine the rate and type of complications during surgery for treatment of chronic subdural hematoma and assess ways for their prevention.&#x0D; Material and Methods: A total of 50 patients of chronic SDH were selected from the Neurosurgery Department of Bahawal Victoria Hospital. Patients were treated surgically with a single burr hole evacuation under local anesthesia, introduced a subdural drain, nursed in a head-down position for 24 hours, and given plenty of fluids orally and intravenous route. The surgical technique involved a formation of a single burr hole at the point of maximum density.&#x0D; Results: Out of 50, 43 patients recovered smoothly postoperatively and discharged on the 7th postoperative day. Two patients were re-operated due to inadequate evacuation or reaccumulation. One patient developed subdural empyema post-operatively and expired in spite of good antibiotic cover. In one patient subdural drain penetrated the brain parenchyma resulting in dysphasia. Another patient formed an intracerebral hematoma due to irrigation of the cavity with pressure. One patient with GCS 4/15 developed seizures postoperatively and expired after one hour. One patient developed gross subdural tension pneumocephalus after removing the subdural drain was re-operated and recovered.&#x0D; Conclusion: Single burr hole evacuation of chronic SDH under local anesthesia is the most accepted surgical treatment. Using proper aseptic surgical techniques, the introduction of the minimum necessary length of the subdural catheter to avoid penetration into the brain parenchyma, followed by careful irrigation of the subdural cavity can help prevent complications.

Listening to pulses of radiation: design of a submersible thermoacoustic sensor

Nowadays, various collaborations are creating immense machines to try to track and understand the origin of high-energy cosmic particles (e.g., IceCube, ANTARES, Baikal-GVD, P-ONE). The detection mechanism of these sophisticated experiments relies mainly on an optical signal generated by the passage of charged particles on a dielectric medium (Čerenkov radiation). Unfortunately, the dim light produced by passing particles cannot travel too far until it fades away, creating the necessity to instrument large areas with short spacing between sensors. The range limitation of the optical technique has created a fertile ground for experimenting on the detection of acoustic signals generated by radiation—thermoacoustics. Despite the increased use of the thermoacoustic technique, the instrumentation to capture the faint acoustic signals is still scarce. Therefore, this work has the objective to contribute with information on the critical stages of an affordable submersible thermoacoustic sensor: namely the piezoelectric transducer and the amplifying electronics. We tested the sensor in a 170,{textit{l}} non-anechoic tank using an infrared (lambda =1064,hbox {nm}) Q-switched Nd:YAG laser as a pulsed energy source to create the characteristic signals of the thermoacoustic phenomena. In accordance with the thermoacoustic model, a polarity inversion of the pressure signal was observed when transiting from temperatures below the point of maximum density of water to temperatures above it. Also, the amplitude of the acoustic signal displayed a linear relationship with pulse energies up to (51.1 pm 1.7),hbox {mJ} (R^2 sim 0.98). Despite the use of cost-effective parts and simple construction methods, the proposed sensor design is a viable instrument for experimental thermoacoustic investigations on high-energy particles.

De Novo Protein Structure Modeling Tool MAINMAST Enhanced for Multiple Chain Complexes and Bound Ligands

The significant progress of the cryo-EM poses a pressing need for software for structural interpretation of EM maps. Particularly, protein structure modeling tools are needed for maps determined around 4 Å resolution, where modeling protein structure in EM map are still challenging problems. We have developed a de novo modeling tool named MAINMAST (MAINchain Model trAcing from Spanning Tree, http://kiharalab.org/mainmast/) for EM maps for this resolution range (Nature Communications, 2018). MAINMAST builds main-chain traces of a protein in an EM map from a tree graph structure constructed by connecting local maximum density points (LDPs)in the EM map. Here, we report the new version of MAINMAST that can handle (1) multiple protein chains with symmetry and (2) proteins with bound ligands in EM maps. For modeling of multiple protein chains, the new MAINMAST automatically identifies pairs of LDPs that locate in symmetric positions. Then, the identified LDP pairs are recorded as a tabu-pair list, which should not be included in a single chain. With the computed restrains in the tabu-pair list, MAINMAST constructs minimum spanning trees, which satisfy the all restrains and will produce symmetric chain structures. Once the initial trees are generated, the trees are optimized, and then the target sequence is mapped. For modeling of proteins with bound ligands, MAINMAST analyzes the tree-graph data and constructs main-chain model, and then detects the ligand-binding sites. Once MAINMAST identify the potential position of the bound ligand, MAINMAST segments the density map around the binding site, and models the ligand structure. We tested the new protocol on 24-mer complexes, apo-ferritin (emd-20026, emd-20027 and emd-20028) and a dimer complex, alcohol dehydrogenase with NAD molecules (emd-0406). MAINMAST built accurate protein structure models and NAD ligand models.

DC to single‐phase AC grid connected inverter with boost‐type active buffer circuit operated in discontinuous current mode

AbstractA novel circuit topology for a single‐phase inverter with a power decoupling capability operated in discontinuous current mode (DCM) is proposed in this paper. An inverter connected to a single‐phase grid requires a power decoupling capability to compensate for a power ripple with twice the grid frequency. Bulky capacitors are used as DC‐link capacitors in conventional systems. In contrast, the proposed circuit topology can use ceramic capacitors instead of electrolytic capacitors by reducing the required capacitance based on the active buffer concept. Moreover, this active buffer requires no additional inductor because it uses DCM for the power decoupling capability. In this paper, a control method for the active buffer circuit operated in DCM is introduced. An experimental verification of a 1‐kW prototype shows that the proposed circuit reduces the input current ripple at twice the grid frequency by 96.8%, with a maximum efficiency of 95.2%. In addition, the Pareto optimization of power density and efficiency is used to clarify the maximum power density points. It is found that the maximum power density of the proposed circuit is 1.6 times higher than that of a conventional boost‐type active buffer.

Generation of a sub-half-wavelength focal spot with purely transverse spin angular momentum

We theoretically demonstrate that optical focus fields with purely transverse spin angular momentum (SAM) can be obtained when a kind of special incident fields is focused by a high numerical aperture (NA) aplanatic lens (AL). When the incident pupil fields are refracted by an AL, two transverse Cartesian components of the electric fields at the exit pupil plane do not have the same order of sinusoidal or cosinoidal components, resulting in zero longitudinal SAMs of the focal fields. An incident field satisfying above conditions is then proposed. Using the Richard–Wolf vectorial diffraction theory, the energy density and SAM density distributions of the tightly focused beam are calculated and the results clearly validate the proposed theory. In addition, a sub-half-wavelength focal spot with purely transverse SAM can be achieved and a flattop energy density distribution parallel to z-axis can be observed around the maximum energy density point.

PEMBUATAN BIODIESEL DARI RBDPO DENGAN KATALIS CANGKANG KEPAH

Biodiesel is a low-emission diesel fuel substitute made from renewable resources and waste oil. The objective of the study was to study of CaO catalysts in biodiesel production from RBDPO with clam shell catalyst through calcinations of CaCO3 with temperature of 900oC and 3.5 hours will be obtained CaO content of 68,35%. Effect of various process variables such as type of catalyst, reaction time, amount of catalyst and molar ratio of Methanol / oil were investigated. The biodiesel properties like methyl ester content, density, viscosity, and flash point was compared with Indonesian Standard (SNI). Under the best condition, the maximum yield, purity, density, viscosity and flash point of biodiesel RBDPO respectively for 84,0179%, 97,98%, 875,47 kg/m3, 4,99 cSt and 122oC was obtained by using 12:1 molar ratio of methanol to RBDPO oil at 60oC, for a reaction time of 2 hours in the presence 5 wt% of CaO catalyst. The results of this research showed that heterogeneous catalysts CaO derived from clam shell suitable to be used as catalysts in biodiesel production.

High-m kink/tearing modes in cylindrical geometry

The global ideal kink equation, for cylindrical geometry and zero beta, is simplified in the high poloidal mode number limit and used to determine the tearing stability parameter, Δ′. In the presence of a steep monotonic current gradient, Δ′ becomes a function of a parameter, σ0, characterising the ratio of the maximum current gradient to magnetic shear and xs, characterising the separation of the resonant surface from the maximum of the current gradient. In equilibria containing a current ‘spike’, so that there is a non-monotonic current profile, Δ′ also depends on two parameters: κ, related to the ratio of the curvature of the current density at its maximum to the magnetic shear and xs, which now represents the separation of the resonance from the point of maximum current density. The relation of our results to earlier studies of tearing modes and to recent gyrokinetic calculations of current driven instabilities, is discussed, together with potential implications for the stability of the tokamak pedestal.

Penetrative Rayleigh-Bénard convection in water near its maximum density point

The presence of a density maximum in water near 4 °C significantly modifies the nature and onset conditions of convective flows due to imposed temperature differences. In the present study, vertical temperature gradients are imposed upon a horizontal, rectangular layer of water, with the top and bottom surfaces maintained above and below the maximum density temperature, respectively. In such an arrangement, convection beginning in the lower, unstable portion of the layer (as small as 1/3 of the layer height) may penetrate into the upper, stable region. The resulting convection patterns are visualized using schlieren or shadowgraph techniques along multiple visual axes. The measured onset conditions and observed patterns are discussed in the context of preceding predictions and experimental observations in similar penetrative systems. As expected from the non-Boussinesq nature of water in this temperature range, convection sets in at temperature differences below those predicted by linear stability theory when the unstable portion of the layer is sufficiently small. The conduction-convection transition is also hysteretic in nature. At onset, the convection pattern consists of parallel, transverse rolls due to the boundary conditions of the fluid chamber. When the unstable portion of the layer is significantly less than half of the fluid layer height, the convective motion is found to penetrate only partway into the upper stable region, within which weakly counter-rotating motions are driven. At higher Rayleigh numbers, the fluid undergoes secondary transitions to either hexagonal cellular or longitudinal roll states which are visualized for the first time. Pattern heights and wavenumbers were measured in some instances, establishing qualitative (in general) and quantitative (over some parameter ranges) agreement with linear theory.

Three-Dimensional Reference Interaction Site Model Self-Consistent Field Study of the Electronic Structure of [Cr(H2O)6]3+ in Aqueous Solution

The three-dimensional reference interaction-site model self-consistent-field (3D-RISM-SCF) method was applied to the electronic structure of hexahydrated chromium trication [Cr(H2O)6](3+) in aqueous solution. The 3D distribution around [Cr(H2O)6](3+) showed 12 maximum density points arising from hydrogen bonds, as well as eight local maximum points at the hollow sites, in the second hydration shell. The 3D distribution function also indicated 20 local maximum sites in the third hydration shell. The low-lying excited states of vertical transitions were computed using time-dependent density functional theory (TD-DFT), including the electric field from the solvent. The electronic configurations and excitation energies calculated using DFT and 3D-RISM-SCF were very similar, although the orbital energies involved in the transition were rather different. The two lowest excited states (1(4)T and 2(4)T) were roughly assigned to the d-d transitions, and the third and fourth excited states (3(4)T and 4(4)T) were assigned to ligand-to-metal charge-transfer transitions. The computed excited energies were in good agreement with the experimental values.

AN OFF-CENTER DENSITY PEAK IN THE MILKY WAY'S DARK MATTER HALO?

We show that the position of the central dark matter density peak may be expected to differ from the dynamical center of the Galaxy by several hundred parsec. In Eris, a high resolution cosmological hydrodynamics simulation of a realistic Milky-Way-analog disk galaxy, this offset is 300 - 400 pc (~3 gravitational softening lengths) after z=1. In its dissipationless dark-matter-only twin simulation ErisDark, as well as in the Via Lactea II and GHalo simulations, the offset remains below one softening length for most of its evolution. The growth of the DM offset coincides with a flattening of the central DM density profile in Eris inwards of ~1 kpc, and the direction from the dynamical center to the point of maximum DM density is correlated with the orientation of the stellar bar, suggesting a bar-halo interaction as a possible explanation. A dark matter density offset of several hundred parsec greatly affects expectations of the dark matter annihilation signals from the Galactic Center. It may also support a dark matter annihilation interpretation of recent reports by Weniger (2012) and Su & Finkbeiner (2012) of highly significant 130 GeV gamma-ray line emission from a region 1.5 degrees (~200 parsec projected) away from Sgr A* in the Galactic plane.