arXiv subjects

Hao Liu

Publications and source records attributed to Hao Liu.

At least 685 records · Page 38Linked to original sources

arXiv2016

Electronic Single Molecule Identification of Carbohydrate Isomers by Recognition Tunneling

Glycans play a central role as mediators in most biological processes, but their structures are complicated by isomerism. Epimers and anomers, regioisomers, and branched sequences contribute to a structural variability that dwarfs those of nucleic acids and proteins, challenging even the most sophisticated analytical tools, such as NMR and mass spectrometry. Here, we introduce an electron tunneling technique that is label-free and can identify carbohydrates at the single-molecule level, offering significant benefits over existing technology. It is capable of analyzing sub-picomole quantities of sample, counting the number of individual molecules in each subset in a population of coexisting isomers, and is quantitative over more than four orders of magnitude of concentration. It resolves epimers not well separated by ion-mobility and can be implemented on a silicon chip. It also provides a readout mechanism for direct single-molecule sequencing of linear oligosaccharides.

physics.chem-ph↗

arXiv2015

The effect of the chiral chemical potential on the chiral phase transition in the NJL model with different regularization schemes

We study the chiral phase transition in the presence of the chiral chemical potential $μ_5$ using the two-flavor Nambu--Jona-Lasinio model. In particular, we analyze the reason why one can obtain two opposite behaviors of the chiral critical temperature as a function of $μ_5$ in the framework of different regularization schemes. We compare the modifications of the chiral condensate and the critical temperature due to $μ_5$ in different regularization schemes, analytically and numerically. Finally, we find that, for the conventional hard-cutoff regularization scheme, the increasing dependence of the critical temperature on the chiral chemical potential is an artifact, which is caused by the fact that it does not include complete contribution from the thermal fluctuations. When the thermal contribution is fully taken into account, the chiral critical temperature should decrease with $μ_5$.

hep-ph↗

arXiv2015

Survival of charged rho condensation at high temperature and density

The charged vector $ρ$ mesons in the presence of external magnetic fields at finite temperature $T$ and chemical potential $μ$ have been investigated in the framework of the Nambu--Jona-Lasinio model. We compute the masses of charged $ρ$ mesons numerically as a function of the magnetic field for different values of temperature and chemical potential. The self-energy of the $ρ$ meson contains the quark-loop contribution, i.e. the leading order contribution in $1/N_c$ expansion. The charged $ρ$ meson mass decreases with the magnetic field and drops to zero at a critical magnetic field $eB_c$, which means that the charged vector meson condensation, i.e. the electromagnetic superconductor can be induced above the critical magnetic field. Surprisingly, it is found that the charged $ρ$ condensation can even survive at high temperature and density. At zero temperature, the critical magnetic field just increases slightly with the chemical potential, which indicates that the charged $ρ$ condensation might occur inside compact stars. At zero density, in the temperature range $0.2-0.5~ {\rm GeV}$, the critical magnetic field for charged $ρ$ condensation is in the range of $0.2-0.6~ {\rm GeV}^2$, which indicates that the high temperature electromagnetic superconductor could be created at LHC.

hep-ph↗

arXiv2015

The Morphology of the Anomalous Microwave Emission in the Planck 2015 data release

We calculate weighted mosaic correlations between the recently published Planck 2015 foreground maps - both anomalous microwave emission (AME) maps, free-free emission, synchrotron radiation and thermal dust emission. The weighting coefficients are constructed taking account of the signal-to-error ratio given by the data product. Positive correlation is found for AME compared with thermal dust emission as well as synchrotron radiation. We find AME and free-free emission tending to be anti-correlated, however, when investigating different scales, their relationship appears to be more complex. We argue that dust particles responsible for AME are pushed out of hot zones in the interstellar medium (ISM).

astro-ph.CO↗

arXiv2015

The Kullback-Leibler Divergence as an Estimator of the Statistical Properties of CMB Maps

The identification of unsubtracted foreground residuals in the cosmic microwave background maps on large scales is of crucial importance for the analysis of polarization signals. These residuals add a non-Gaussian contribution to the data. We propose the Kullback-Leibler (KL) divergence as an effective, non-parametric test on the one-point probability distribution function of the data. With motivation in information theory, the KL divergence takes into account the entire range of the distribution and is highly non-local. We demonstrate its use by analyzing the large scales of the Planck 2013 SMICA temperature fluctuation map and find it consistent with the expected distribution at a level of 6%. Comparing the results to those obtained using the more popular Kolmogorov-Smirnov test, we find the two methods to be in general agreement.

astro-ph.CO↗

arXiv2015

The Complete Weight Enumerator of A Class of Linear Codes

Linear codes can be employed to construct authentication codes, which is an interesting area of cryptography. The parameters of the authentication codes depend on the complete weight enumerator of the underlying linear codes. In order to obtain an authentication code with good parameters, the underlying linear code must have proper parameters. The first objective of this paper is to determine the complete weight enumerators of a class of linear codes with two weights and three weights. The second is to employ these linear codes to construct authentication codes with new parameters.

cs.IT↗

arXiv2015

Mechanical properties of jammed packings of frictionless spheres under applied shear stress

By minimizing a thermodynamic-like potential, we unbiasedly sample the potential energy landscape of soft and frictionless spheres under constant shear stress. We obtain zero-temperature jammed states under desired shear stresses and investigate their mechanical properties as a function of the shear stress. As a comparison, we also obtain jammed states from the quasistatic-shear sampling in which the shear stress is not well-controlled. Although the yield stresses determined by both samplings show the same power-law scaling with the compression from point $J$, i.e.~the jamming transition point at zero temperature and shear stress, for finite size systems, the quasistatic-shear sampling leads to a lower yield stress and a higher critical volume fraction of point $J$. The shear modulus of jammed solids decreases when increasing the shear stress. However, the shear modulus does not decay to zero at yielding. This discontinuous change of the shear modulus implies the discontinuous nature of the unjamming transition under nonzero shear stress, which is further verified by the observation of a discontinuous jump of the pressure from jammed solids to shear flows. The pressure jump decreases upon decompression and approaches zero at the critical-like point $J$, in analogy with well-known phase transitions under external field. The analysis of force networks in jammed solids reveals that the force distribution is more sensitive to the increase of the shear stress near point $J$. The force network anisotropy increases with the shear stress. Weak particle contacts near the average force and under large shear stresses exhibit asymmetric angle distribution.

cond-mat.soft↗

arXiv2014

Spontaneous generation of local CP violation and inverse magnetic catalysis

In the chiral symmetric phase, the polarized instanton--anti-instanton molecule pairing induces a nontrivial repulsive interaction in the iso-scalar axial-vector channel. As a consequence, one unusual property is observed that in the chiral restoration phase, there is a first order phase transition for the spontaneous generation of local CP violation and chiral imbalance. Furthermore, it is found that external magnetic fields will lower the critical temperature for the local CP-odd phase transition and catalyze the chiral imbalance, which destroys the chiral condensate with pairing quarks between different chiralities. A reasonable strength of the repulsive interaction in the iso-scalar axial-vector channel can naturally explain the inverse magnetic catalysis around the critical temperature under external magnetic fields.

hep-ph↗

arXiv2014

Charged and neutral vector meson under magnetic field

The vector meson $ρ$ in the presence of external magnetic field has been investigated in the framework of the Nambu--Jona-Lasinio model, where mesons are constructed by infinite sum of quark-loop chains by using random phase approximation. The $ρ$ meson polarization function is calculated to the leading order of $1/N_c$ expansion. It is found that the constituent quark mass increases with magnetic field, the masses of the neutral vector meson $ρ^{0}$ with spin component $s_z=0,\,\pm1$ and the charged vector meson $ρ^{\pm}$ with $s_z=0$ also increases with magnetic field. However, the mass square of the charged vector meson $ρ^{+}$ ($ρ^{-}$) with $s_z=+1$ ($s_z=-1$) decreases linearly with magnetic field and drops to zero at the critical magnetic field $e B_c \simeq 0.2 {\rm GeV}^2$, which indicates the possible condensation of charged vector meson in the vacuum. This critical magnetic field is much lower than the value $eB_c=0.6 {\rm GeV}^2$ predicted by a point-like vector meson. We also show that if we use lowest Landau level approximation, the mass of the charged vector meson $ρ^{\pm}$ for $s_z=\pm1$ cannot drop to zero at high magnetic fields.

hep-ph↗

arXiv2014

Fingerprints of Galactic Loop I on the Cosmic Microwave Background

We investigate possible imprints of galactic foreground structures such as the "radio loops" in the derived maps of the cosmic microwave background. Surprisingly there is evidence for these not only at radio frequencies through their synchrotron radiation, but also at microwave frequencies where emission by dust dominates. This suggests the mechanism is magnetic dipole radiation from dust grains enriched by metallic iron or ferrimagnetic materials. This new foreground we have identified is present at high galactic latitudes, and potentially dominates over the expected $B$-mode polarization signal due to primordial gravitational waves from inflation.

astro-ph.CO↗

arXiv2014

Femtosecond pulse generation from a Topological Insulator mode-locked fiber laser

We reported on the generation of femtosecond pulse in an anomalous-dispersion fiber ring laser by using a polyvinyl alcohol (PVA)-based Topological Insulator (TI), Bi2Se3 saturable absorber (SA). The PVA-TI composite has a low saturable optical intensity of 12 MW/cm2 and a modulation depth of ~3.9%. By incorporating the fabricated PVA-TISA into a fiber laser, mode-locking operation could be achieved at a low pump threshold of 25 mW. After an optimization of the cavity parameters, optical pulse with ~660 fs centered at 1557.5 nm wavelength had been generated. The experimental results demonstrate that the PVA could be an excellent host material for fabricating high-performance TISA, and also indicate that the filmy PVA-TISA is indeed a good candidate for ultrafast saturable absorption device.

physics.optics↗

arXiv2014

Uncovering the information core in recommender systems

With the rapid growth of the Internet and overwhelming amount of information that people are confronted with, recommender systems have been developed to effiectively support users' decision-making process in online systems. So far, much attention has been paid to designing new recommendation algorithms and improving existent ones. However, few works considered the different contributions from different users to the performance of a recommender system. Such studies can help us improve the recommendation efficiency by excluding irrelevant users. In this paper, we argue that in each online system there exists a group of core users who carry most of the information for recommendation. With them, the recommender systems can already generate satisfactory recommendation. Our core user extraction method enables the recommender systems to achieve 90% of the accuracy by taking only 20% of the data into account.

cs.IR↗

arXiv2014

Information Filtering via Collaborative User Clustering Modeling

The past few years have witnessed the great success of recommender systems, which can significantly help users find out personalized items for them from the information era. One of the most widely applied recommendation methods is the Matrix Factorization (MF). However, most of researches on this topic have focused on mining the direct relationships between users and items. In this paper, we optimize the standard MF by integrating the user clustering regularization term. Our model considers not only the user-item rating information, but also takes into account the user interest. We compared the proposed model with three typical other methods: User-Mean (UM), Item-Mean (IM) and standard MF. Experimental results on a real-world dataset, \emph{MovieLens}, show that our method performs much better than other three methods in the accuracy of recommendation.

cs.IR↗

arXiv2013

Finite size analysis of zero-temperature jamming transition under applied shear stress

By finding local minima of an enthalpy-like energy, we can generate jammed packings of frictionless spheres under constant shear stress $σ$ and obtain the yield stress $σ_y$ by sampling the potential energy landscape. For three-dimensional systems with harmonic repulsion, $σ_y$ satisfies the finite size scaling with the limiting scaling relation $σ_y\simϕ- ϕ_{_{c,\infty}}$, where $ϕ_{_{c,\infty}}$ is the critical volume fraction of the jamming transition at $σ=0$ in the thermodynamic limit. The width or uncertainty of the yield stress decreases with decreasing $ϕ$ and decays to zero in the thermodynamic limit. The finite size scaling implies a length $ξ\sim (ϕ-ϕ_{_{c,\infty}})^{-ν}$ with $ν=0.81\pm 0.05$, which turns out to be a robust and universal length scale exhibited as well in the finite size scaling of multiple quantities measured without shear and independent of particle interaction. Moreover, comparison between our new approach and quasi-static shear reveals that quasi-static shear tends to explore low-energy states.

cond-mat.soft↗

arXiv2013

Evidence of s-channel Single Top Quark Production in Events with one Charged Lepton and Bottom Quark Jets at CDF

We report an evidence of \textit{s}-channel single top quark production in $p\bar{p}$ collision at $\sqrt{s}= 1.96 \mathrm{TeV}$ using data with integrated luminosity of $9.4 \mathrm{fb}^{-1}$ collected by the Collider Detector at Fermilab (CDF). We select events with one charged lepton, large missing transverse energy and two bottom quark jets. The observed significance of the result is 3.8 standard deviation from background only prediction. We measure the inclusive cross section to be $1.41^{+0.44}_{-0.42}\mathrm{(stat+syst)} \mathrm{pb}$ assuming $m_t = 172.5 \mathrm{GeV}/c^2$.

hep-ex↗

arXiv2013

Large-scale anomalies of the CMB in the curvaton scenario

We extend the curvaton scenario presented by Erickcek et al. (2008, 2009), to explain how the even-odd multipole asymmetry of the Cosmic Microwave Background (CMB) (also called parity asymmetry, (Kim & Naselsky 2010)) and power anisotropies can be generated by the curvaton field, which acts as an extra component to the spectrum of adiabatic perturbations in the inflationary epoch. Our work provides a possible cosmic explanation to the CMB large-scale asymmetry problems besides systematics and unknown residuals.

astro-ph.CO↗

arXiv2013

Consistency tests for Planck and WMAP in the low multipole domain

Recently, full sky maps from Planck have been made publicly available. In this paper, we do consistency tests for the three Planck CMB sky maps. We assume that the difference between two maps represents the contributions from systematics, noise, foregrounds and other sources, and that a precise representation of the Cosmic Microwave Background should be uncorrelated with it. We investigate the cross correlation in pixel space between the difference maps and the various Planck maps and find no significant correlations, in comparison to 10000 random Gaussian simulated maps. Additionally we investigate the difference map between the WMAP ILC 9 year map and the ILC 7 year map. We perform cross correlations between this difference map, and the ILC9 and ILC7, and find significant correlations only for the ILC9, at more than the 99.99% level. Likewise, a comparison between the Planck NILC map and the WMAP ILC9 map, shows a strong correlation for the ILC9 map with the difference map, also at more than the 99.99% level. Thus the ILC9 appears to be more contaminated than the ILC7, which should be taken into consideration when using WMAP maps for cosmological analyses.

astro-ph.CO↗

arXiv2013

Missing completely of CMB quadrupole in WMAP data

In cosmic microwave background (CMB) experiments, foreground-cleaned temperature maps are still contaminated by the residual dipole due to uncertainties of the Doppler dipole direction and microwave radiometer sidelobe. To obtain reliable CMB maps, such contamination has to be carefully removed from observed data. We have previously built a software package for map-making, residual dipole-contamination removal, and power spectrum estimation from the Wilkinson Microwave Anisotropy Probe (WMAP) raw data. This software has now been significantly improved. With the improved software, we obtain a negative result of CMB quadrupole detection with the WMAP raw data, which is -3.2+-3.5 uK^2 from the seven-year WMAP (WMAP7) data. This result is evidently incompatible with ~1000 uK^2 expected from the standard cosmological model LCDM. The completely missing of CMB quadrupole poses a serious challenge to the standard model and sets a strong constraint on possible models of cosmology. Due to the importance of this result for understanding the origin and early evolution of our universe, the software codes we used are opened for public checking.

astro-ph.CO↗