Mass Density Fluctuations Research Articles

Dielectric Metasurface Enabled Compact, Single-Shot Digital Holography for Quantitative Phase Imaging.

Quantitative phase imaging (QPI) enables nondestructive, real-time, label-free imaging of transparent specimens and can reveal information about their fundamental properties such as cell size and morphology, mass density, particle dynamics, and cellular fluctuations. Development of high-performance and low-cost quantitative phase imaging systems is thus required in many fields, including on-site biomedical imaging and industrial inspection. Here, we propose an ultracompact, highly stable interferometer based on a single-layer dielectric metasurface for common path off-axis digital holography and experimentally demonstrate quantitative phase imaging. The interferometric imaging system leveraging an ultrathin multifunctional metasurface captures image plane holograms in a single shot and provides quantitative phase information on the test samples for extraction of its physical properties. With the benefits of planar engineering and high integrability, the proposed metasurface-based method establishes a stable miniaturized QPI system for reliable and cost-effective point-of-care devices, live cell imaging, 3D topography, and edge detection for optical computing.

Dayside Upper‐Thermospheric Density Fluctuations as Observed by GRACE and GRACE‐FO at ∼500 km Height

AbstractWe statistically investigate fluctuation amplitudes (normalized to the background values) of dayside low‐/mid‐latitude upper‐thermospheric mass density as observed by the Gravity Recovery and Climate Experiment (GRACE) and GRACE‐Follow‐On (GRACE‐FO) spacecraft at ∼500 km altitude between 2002 and 2022. There are three new findings in our results. First, the climatology closely replicates previous studies on stratospheric and upper‐thermospheric gravity waves (GWs) below the GRACE(‐FO) altitudes. For example, in low‐latitude regions, the fluctuations are stronger above continents than in the oceanic area. Mid‐latitude fluctuations prefer the local winter hemisphere to the summer, and the South American/Atlantic region in June solstice hosts stronger fluctuations than in any other low‐/mid‐latitude locations or seasons. Fluctuations are more intense under lower solar activity. The above‐mentioned consistency of the GRACE(‐FO) results with previous lower‐altitude GW studies confirms that GWs can penetrate up to 500 km. Second, the anti‐correlation of upper‐thermospheric GW with solar activity, which has been earlier reported for multi‐year time scales, can also be identified on the scale of the solar rotation period (∼27 days). Third, we demonstrate asymmetry between pre‐noon and post‐noon GWs. The former exhibits stronger GW activity, which may result from the colder thermosphere being more favorable for intense mass density fluctuations via secondary/tertiary GW generation.

Photonics probing of pup brain tissue and molecular-specific nuclear nanostructure alterations due to fetal alcoholism via light scattering/localization approaches.

.Significance: Light is a good probe for studying the nanoscale-level structural or molecular-specific structural properties of brain cells/tissue due to stress, alcohol, or any other abnormalities. Chronic alcoholism during pregnancy, i.e., fetal alcoholism, being teratogenic, results in fetal alcohol syndrome, and other neurological disorders. Understanding the nano-to-submicron scale spatial structural properties of pup brain cells/tissues using light/photonic probes could provide a plethora of information in understanding the effects of fetal alcoholism.Aim: Using both light scattering and light localization techniques to probe alterations in nano- to-submicron scale mass density or refractive index fluctuations in brain cells/tissues of mice pups, exposed to fetal alcoholism.Approach: We use the mesoscopic physics-based dual spectroscopic imaging techniques, partial wave spectroscopy (PWS) and molecular-specific inverse participation ratio (IPR) using confocal imaging, to quantify structural alterations in brain tissues and chromatin/histone in brain cells, respectively, in 60 days postnatal mice pup brain, exposed to fetal alcoholism.Results: The finer focusing PWS analysis on tissues shows an increase in the degree of structural disorder strength in the pup brain tissues. Furthermore, results of the molecular-specific light localization IPR technique show an increase in the degree of spatial molecular mass density structural disorder in DNA and a decrease in the degree in histone.Conclusions: In particular, we characterize the spatial pup brain structures from the molecular to tissue levels and address the plausible reasons for such as mass density fluctuations in fetal alcoholism.

The effect of ultrasmall grain sizes on the thermal conductivity of nanocrystalline silicon thin films

Nanocrystallization has been an important approach for reducing thermal conductivity in thermoelectric materials due to limits on phonon mean-free path imposed by the characteristic structural size. We report on thermal conductivity as low as 0.3 Wm−1K−1 of nanocrystalline silicon thin films prepared by plasma-enhanced chemical-vapor deposition as grain size is reduced to 2.8 nm by controlling hydrogen dilution of silane gas during growth. A multilayered film composed by alternating growth conditions, with layer thicknesses of 3.6 nm, is measured to have a thermal conductivity 30% and 15% lower than its two constituents. Our quantitative analysis attributes the strong reduction of thermal conductivity with decreasing grain size to the magnifying effect of porosity which occurs concomitantly due to increased mass density fluctuations. Our results demonstrate that ultrasmall grain sizes, multilayering, and porosity, all at a similar nanometer-size scale, may be a promising way to engineer thermoelectric materials.

Effect of the Coupling Between Director and Mass Density Fluctuations on the Paranematic–Nematic Transition Temperature: A Mean-field Treatment

It has experimentally verified that the variation of the paranematic–nematic transition temperature follows the relation $$\Delta T_{PN}^{}=m E$$ for low electric fields. Values of the coefficient m are found to be positive and negative. Previous work, on the basis of a simple physical model supplemented by dimensional argument, attributed this behavior to the quenching of long-wavelength director fluctuations due to the field. In this paper, we show that the Landau–de Gennes theory predicts $$\Delta T_{PN}^{}\propto E^2$$ even when the quenching of director fluctuations is considered. Based on a recent generalization of the Landau–de Gennes theory that incorporates mass density fluctuations, we give a mean-field treatment of the coupling between director and mass density fluctuations and calculate the contribution of this mechanism to the Helmholtz free energy. Interestingly, the expression we obtain for $$\Delta T_{PN}^{}$$ is in good quantitative agreement with what is experimentally observed. In particular, it explains why m takes values of both signs.

Photonic probing of structural alterations in DNA specific mass density fluctuations in nuclei due to total body irradiation (TBI) via confocal imaging

Abnormalities within cells result in intracellular structural alterations ranging from nano to submicron scales. Accidental or deliberate exposure to total body irradiation has adverse effects on the nuclear DNAs of cells. Here, we study the molecular specific DNA spatial mass density fluctuations of chromatin of mice gut cell nuclei caused by the exposure to standard doses of 4-Gy total body irradiation, using the light localization technique called inverse participation ratio via confocal imaging. Results show radiation suppresses DNA spatial mass density fluctuations. And hence, the reduction and saturation in DNA mass density fluctuations are observed on different durations of post-irradiation.

Spectroscopic Study on Pseudomonas Aeruginosa Biofilm in the Presence of the Aptamer-DNA Scaffolded Silver Nanoclusters.

We report the effectiveness of silver nanocluster (Ag-NC) against the biofilm of Pseudomonas aeruginosa (PA). Two DNA aptamers specific for PA and part of their sequences were chosen as templates for growing the Ag-NC. While circular dichroism (CD) studies determined the presence of secondary structures, UV/Vis absorption, and fluorescence spectroscopic studies confirmed the formation of the fluorescent Ag-NC on the DNA templates. Furthermore, mesoscopic physics-based partial wave spectroscopy (PWS) was used to analyze the backscattered light signal that can detect the degree of nanoscale mass density/refractive index fluctuations to identify the biofilm formation, comparatively among the different aptamers with respect to the control sample. The importance of the secondary structure of the aptamer DNA in targeting, successfully binding with the cells and delivering the Ag-NC, is evidenced by the decrease in disorder strength (Ld) of the Ag-NC treated samples compared to the untreated PA cells, which showed the abundance of higher Ld in the PWS studies. The higher Ld value attributed to the higher mass density fluctuations and the formation of biofilm. We envision this study to open a new avenue in using a powerful optical microscopic technique like PWS in detection, and DNA aptamer enclosed silver nanoclusters to prevent biofilms for opportunist pathogens like Pseudomonas aeruginosa.

Inclusion of Mass Density Fluctuations in the Landau-de Gennes Theory of Nematic-Isotropic Phase Transition

Experimental evidences have shown that mass density gradients couple energetically to the liquid crystal director. In this paper, we incorporate this mechanism into the Landau-de Gennes theory of nematic-isotropic transition. In conformity with empirical evidence, the extended theory enables us to explain the enhancement to the amplitude of the singular part of the specific heat above the nematic-isotropic phase transition temperature TNI. It also permits us to obtain a correction term for the Kerr constant B in isotropic phase proportional to 1/(T − T∗)2, where T∗ is the virtual transition temperature. The curve B versus T thus corrected provides a very good fit to experimental data.

Jeans surface instability of an electron-ion plasma

The dispersive properties of Jeans surface instability at a charged plane interface of weakly coupled, classical self-gravitating, magnetized electron-ion plasma and vacuum, are investigated. The general dispersion relation is formulated by employing one fluid magnetohydrodynamic (MHD) model and Poisson’s equations for both electrostatic and gravitational potentials. It is shown that both the surface charge and mass density fluctuations are coupled together effectively, to enhance the growth rate of surface Jeans instability, whereas an increase in magnetic field and surface tension tends to stabilize Jeans surface instability. The modified Jeans criterion of gravitational instability is obtained by formulating a new definition of Jeans wavelength. These results may be useful to examine the gravitational collapse of self-gravitating electron-ion plasma, leading to star formation in astro-cosmic environments.

Field theory of the correlation function of mass density fluctuations for self-gravitating systems

The mass density distribution of Newtonian self-gravitating systems is studied analytically in the field theoretical method. Modeling the system as a fluid in hydrostatic equilibrium, we apply Schwinger’s functional derivative on the average of the field equation of mass density, and obtain the field equation of 2-point correlation function ξ(r) of the mass density fluctuation, which includes the next order of nonlinearity beyond the Gaussian approximation. The 3-point correlation occurs hierarchically in the equation, and is cut off by the Groth-Peebles ansatz, making it closed. We perform renormalization and write the equation with three nonlinear coefficients. The equation tells us that ξ depends on the point mass m and the Jeans wavelength scale λ0, which are different for galaxies and clusters. Applying this to large scale structures, it predicts that the profile of ξcc for clusters is similar to ξgg for galaxies but with a higher amplitude, and that the correlation length increases with the mean separation between clusters, i.e., a scaling behavior r0 ≃ 0.4d. The solution yields the galaxy correlation ξgg(r) ≃ (r0/r)1.7 valid only in a range 1 < r < 10 h−1 Mpc. At larger scales the solution ξgg deviates below the power law and goes to zero around ∼50 h−1 Mpc, just as the observations show. We also derive the field equation of the 3-point correlation function in the Gaussian approximation and its analytical solution, for which the Groth-Peebles ansatz with Q = 1 holds.

Clinical significance of MUC13 in pancreatic ductal adenocarcinoma

BackgroundPoor prognosis of pancreatic cancer (PanCa) is associated with lack of an effective early diagnostic biomarker. This study elucidates significance of MUC13, as a diagnostic/prognostic marker of PanCa. MethodsMUC13 was assessed in tissues using our in-house generated anti-MUC13 mouse monoclonal antibody and analyzed for clinical correlation by immunohistochemistry, immunoblotting, RT-PCR, computational and submicron scale mass-density fluctuation analyses, ROC and Kaplan Meir curve analyses. ResultsMUC13 expression was detected in 100% pancreatic intraepithelial neoplasia (PanIN) lesions (Mean composite score: MCS = 5.8; AUC >0.8, P < 0.0001), 94.6% of pancreatic ductal adenocarcinoma (PDAC) samples (MCS = 9.7, P < 0.0001) as compared to low expression in tumor adjacent tissues (MCS = 4, P < 0.001) along with faint or no expression in normal pancreatic tissues (MCS = 0.8; AUC >0.8; P < 0.0001). Nuclear MUC13 expression positively correlated with nodal metastasis (P < 0.05), invasion of cancer to peripheral tissues (P < 0.5) and poor patient survival (P < 0.05; prognostic AUC = 0.9). Submicron scale mass density and artificial intelligence based algorithm analyses also elucidated association of MUC13 with greater morphological disorder (P < 0.001) and nuclear MUC13 as strong predictor for cancer aggressiveness and poor patient survival. ConclusionThis study provides significant information regarding MUC13 expression/subcellular localization in PanCa samples and supporting the use anti-MUC13 MAb for the development of PanCa diagnostic/prognostic test.

Global-density fluctuations in methane clathrate hydrates in externally applied electromagnetic fields.

Non-equilibrium molecular-dynamics simulations of bulk methane clathrate hydrates have been conducted in a range of externally applied electromagnetic (e/m) fields. Studies into frequencies of system(or "global")-mass-density fluctuations showed that these clathrates have three major modes: the dominant one is attributable to water molecules' librations and occurs at 720 cm-1, regardless of any applied e/m fields. One of the more minor system-density fluctuations arises at 10-12 cm-1 and is caused by the propagation of local-density fluctuations; again, this is independent of e/m fields. The final density fluctuation is caused by e/m fields, and it only becomes apparent for field strengths of 1.2 V/nm or higher. The frequency of this mode is always twice the frequency of the applied e/m field. It was shown that the main qualitative features of the translational and librational densities of states (DOSs) were unaffected by the application of e/m fields; however, a slight coupling effect was observed, producing a peak in all DOSs at the frequency of the applied field. This study showed that e/m fields below a certain intensity threshold do not lead to any marked structural distortion or dissociation effect on pre-existing bulk clathrates, in which the hydrogen-bonding structure of the lattice remains intact. This is verified by system-density and configurational-energy values as well as radial distribution functions.

Mass density fluctuations in quantum and classical descriptions of liquid water.

First principles molecular dynamics simulation protocol is established using revised functional of Perdew-Burke-Ernzerhof (revPBE) in conjunction with Grimme's third generation of dispersion (D3) correction to describe the properties of water at ambient conditions. This study also demonstrates the consistency of the structure of water across both isobaric (NpT) and isothermal (NVT) ensembles. Going beyond the standard structural benchmarks for liquid water, we compute properties that are connected to both local structure and mass density fluctuations that are related to concepts of solvation and hydrophobicity. We directly compare our revPBE results to the Becke-Lee-Yang-Parr (BLYP) plus Grimme dispersion corrections (D2) and both the empirical fixed charged model (SPC/E) and many body interaction potential model (MB-pol) to further our understanding of how the computed properties herein depend on the form of the interaction potential.

Light localization properties of weakly disordered optical media using confocal microscopy: application to cancer detection.

We have developed a novel technique to quantify submicron scale mass density fluctuations in weakly disordered heterogeneous optical media using confocal fluorescence microscopy. Our method is based on the numerical evaluation of the light localization properties of an 'optical lattice' constructed from the pixel intensity distributions of images obtained with confocal fluorescence microscopy. Here we demonstrate that the technique reveals differences in the mass density fluctuations of the fluorescently labeled molecules between normal and cancer cells, and that it has the potential to quantify the degree of malignancy of cancer cells. Potential applications of the technique to other disease situations or characterizing disordered samples are also discussed.

Quantitative analysis of nanoscale intranuclear structural alterations in hippocampal cells in chronic alcoholism via transmission electron microscopy imaging

Chronic alcoholism is known to alter the morphology of the hippocampus, an important region of cognitive function in the brain. Therefore, to understand the effect of chronic alcoholism on hippocampal neural cells, we employed a mouse model of chronic alcoholism and quantified intranuclear nanoscale structural alterations in these cells. Transmission electron microscopy (TEM) images of hippocampal neurons were obtained, and the degree of structural alteration in terms of mass density fluctuation was determined using the light-localization properties of optical media generated from TEM imaging. The results, which were obtained at length scales ranging from ~30 to 200 nm, show that 10–12 week-old mice fed a Lieber–DeCarli liquid (alcoholic) diet had a higher degree of structural alteration than control mice fed a normal diet without alcohol. The degree of structural alteration became significantly distinguishable at a sample length of ~100 nm, which is the typical length scale of the building blocks of cells, such as DNA, RNA, proteins and lipids. Interestingly, different degrees of structural alteration at such length scales suggest possible structural rearrangement of chromatin inside the nuclei in chronic alcoholism.

Occupation times of long-range exclusion and connections to KPZ class exponents

With respect to a class of long-range exclusion processes on $${\mathbb {Z}}^d$$ , with single particle transition rates of order $$|\cdot |^{-(d+\alpha )}$$ , starting under Bernoulli invariant measure $$\nu _\rho $$ with density $$\rho $$ , we consider the fluctuation behavior of occupation times at a vertex and more general additive functionals. Part of our motivation is to investigate the dependence on $$\alpha $$ , d and $$\rho $$ with respect to the variance of these functionals and associated scaling limits. In the case the rates are symmetric, among other results, we find the scaling limits exhaust a range of fractional Brownian motions with Hurst parameter $$H\in [1/2,3/4]$$ . However, in the asymmetric case, we study the asymptotics of the variances, which when $$d=1$$ and $$\rho =1/2$$ points to a curious dichotomy between long-range strength parameters $$0<\alpha \le 3/2$$ and $$\alpha >3/2$$ . In the former case, the order of the occupation time variance is the same as under the process with symmetrized transition rates, which are calculated exactly. In the latter situation, we provide consistent lower and upper bounds and other motivations that this variance order is the same as under the asymmetric short-range model, which is connected to KPZ class scalings of the space-time bulk mass density fluctuations.

Field equation of the correlation function of mass-density fluctuations for self-gravitating systems

We study the mass density distribution of Newtonian self-gravitating systems. Modeling the system as a fluid in hydrostatical equilibrium, we obtain from first principle the field equation and its solution of correlation function $\xi(r)$ of the mass density fluctuation itself. We apply thid to studies of the large-scale structure of the Universe within a small redshift range. The equation tells that $\xi(r)$ depends on the point mass $m$ and the Jeans wavelength scale $\lambda_{0}$, which are different for galaxies and clusters. It explains several longstanding, prominent features of the observed clustering : that the profile of $\xi_{cc}(r)$ of clusters is similar to $\xi_{gg}(r)$ of galaxies but with a higher amplitude and a longer correlation length, and that the correlation length increases with the mean separation between clusters as a universal scaling $r_0\simeq 0.4d$. Our solution $\xi(r)$ also yields the observed power-law correlation function of galaxies $\xi_{gg}(r)\simeq (r_0/r)^{1.7}$ valid only in a range $1<r<10 h^{-1}$Mpc. At larger scales the solution $\xi(r)$ breaks below the power law and goes to zero around $\sim 50h^{-1}$Mpc, just as the observational data have demonstrated. With a set of fixed model parameters, the solutions $\xi_{gg}(r)$ for galaxies, the corresponding power spectrum, and $\xi_{cc}(r)$ for clusters, simultaneously, agree with the observational data from the major surveys of galaxies, and of clusters.

Plasma density undulations correlated with thermospheric neutral mass density in the daytime low‐latitude to midlatitude topside ionosphere

AbstractPlasma density undulations in the dayside low‐latitude/midlatitude ionospheric F region were often attributed to thermospheric gravity waves (TGWs). However, the relationship between the former and the latter has been at best indirectly evidenced. In this study we investigate daytime fluctuations in neutral mass density (ρ) and plasma density (ne) measured onboard CHAMP from 2001 to 2010. A significant amount of daytime fluctuations in ne is strongly correlated with in situ fluctuations of ρ, which we term “TGW‐related ne fluctuations.” The TGW‐related ne fluctuations are (1) stronger in the winter hemisphere than in the summer hemisphere and (2) strongest in the South American sector during June solstice months. These climatological features are in general agreement with those of TGWs reported previously, especially at midlatitudes. On the other hand, the relative amplitude of TGW‐related ne fluctuations does not depend strongly on solar activity.

Probing a gravitational cat state

We investigate the nature of a gravitational two-state system (G2S) in the simplest setup in Newtonian gravity. In a quantum description of matter a single motionless massive particle can in principle be in a superposition state of two spatially separated locations. This superposition state in gravity, or gravitational cat state, would lead to fluctuations in the Newtonian force exerted on a nearby test particle. The central quantity of importance for this inquiry is the energy density correlation. This corresponds to the noise kernel in stochastic gravity theory, evaluated in the weak field nonrelativistic limit. In this limit quantum fluctuations of the stress–energy tensor manifest as the fluctuations of the Newtonian force. We describe the properties of such a G2S system and present two ways of measuring the cat state for the Newtonian force, one by way of a classical probe, the other a quantum harmonic oscillator. Our findings include: (i) mass density fluctuations persist even in single particle systems, and they are of the same order of magnitude as the mean; (ii) a classical probe generically records a non-Markovian fluctuating force; (iii) a quantum probe interacting with the G2S system may undergo Rabi oscillations in a strong coupling regime. This simple prototypical gravitational quantum system could provide a robust testing ground to compare predictions from alternative quantum theories, since the results reported here are based on standard quantum mechanics and classical gravity.

Nonlocal halo bias with and without massive neutrinos

Understanding the biasing between the clustering properties of halos and the underlying dark matter distribution is important for extracting cosmological information from ongoing and upcoming galaxy surveys. While on sufficiently large scales the halo overdensity is a local function of the mass density fluctuations, on smaller scales the gravitational evolution generates nonlocal terms in the halo density field. We characterize the magnitude of these contributions at third order in perturbation theory by identifying the coefficients of the nonlocal invariant operators, and extend our calculation to include nonlocal (Lagrangian) terms induced by a peak constraint. We apply our results to describe the scale dependence of halo bias in cosmologies with massive neutrinos. The inclusion of gravity-induced nonlocal terms and, especially, a Lagrangian ${k}^{2}$ contribution is essential to reproduce the numerical data accurately. We use the peak-background split to derive the numerical values of the various bias coefficients from the excursion set peak mass function. For neutrino masses in the range $0\ensuremath{\le}\ensuremath{\sum}_{i}{m}_{{\ensuremath{\nu}}_{i}}\ensuremath{\le}0.6\text{ }\text{ }\mathrm{eV}$, we are able to fit the data with a precision of a few percents up to $k=0.3h\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ without any free parameter.