arXiv subjects

Priyanka Kumari

Publications and source records attributed to Priyanka Kumari.

13 recordsLinked to original sources

arXiv2026

Landau theory applied to antiferroelectric ordering in ferroelectric nematic liquid crystals

The polarization and density modulation associated with antiferroelectric ordering is studied experimentally as a function of temperature in two ferroelectric nematic liquid crystals, the prototypical single compound (DIO) and a commercial mixture (FNLC919). The modulation wavenumber qA is determined by small angle X-ray diffraction from the weak smectic-like density wave (wavenumber qS = 2qA) that accompanies the polarization modulation. Results for qS and the saturated value of the polarization are analyzed in terms of Landau theory previously developed to describe the para-/antiferro-/feroelectric sequence of phase transitions in solid ferroelectrics. The analysis indicates that the polarization modulation is reasonably well approximated by a simple sinusoid in the antiferroelectric phase of DIO, whereas in FNLC919 the modulation develops a strongly soliton-like profile (with sharply decreasing wavenumber) close to the antiferro- to ferrolectric transition.

cond-mat.soft↗

arXiv2025

Helix alignment, chevrons, and edge dislocations in twist-bend ferroelectric nematics

We explore surface alignment and edge dislocations in the recently discovered twist-bend ferroelectric nematic, NTBF, in which the vector of spontaneous polarization follows an oblique helicoidal trajectory around a polar twist-bend axis. In a planar cell, the polar axis aligns at some angle to the rubbing direction to mitigate surface electric charge. We demonstrate that the pseudolayers in planar cells form chevron defects, a hallmark defect of one-dimensionally positionally ordered phases, such as smectic A and smectic C. The polar character of the twist-bend axis prevents the cores of NTBF edge dislocations from splitting into semi-integer disclinations, in stark contrast to dislocations in paraelectric and ferroelectric chiral nematics. The tilt of pseudolayers around the defect core allows us to estimate the elastic penetration length as being close to the pitch of NTBF. Compression/dilation stresses around the core modify the heliconical tilt angle of molecules as evidenced by a substantial variation in local birefringence. The climb of dislocations exhibits high mobility, allowing the system to equilibrate the temperature-dependent pitch. The uncovered properties facilitate the development of NTBF materials for electro-optical applications, such as electrically controlled diffraction lattices and structural colors.

cond-mat.soft↗

arXiv2025

Twist, splay, and uniform domains in ferroelectric nematic liquid crystals

The newly-discovered ferroelectric nematic liquid crystal exhibits a variety of unique defect phenomena. The depolarization field in the material favors spontaneous spatial variations in polarization, manifesting in diverse forms such as bulk twists and arrangements of alternating polarization domains. The configuration of these domains is governed by a balance between depolarization field reduction and molecular alignment at interfaces. We investigate a ferroelectric nematic confined in a thin cell with apolar surface anchoring, patterned using photoalignment. Under uniform planar alignment, the system forms stripes, while a radial +1 defect pattern results in pie-slice domains. Neighboring domains show either opposite directions of uniform polarization (thin cells) or opposite handedness of the spontaneous twist (thick cells). Our calculations and experiments demonstrate that electrostatic interactions tend to shrink domain size, whereas elastic and surface anchoring effects promote larger domains. In this work, we make predictions and measurements of the domain size as a function of cell thickness, and show that ionic screening suppresses domain formation.

cond-mat.soft↗

arXiv2025

A UNet Model for Accelerated Preprocessing of CRISM Hyperspectral Data for Mineral Identification on Mars

Accurate mineral identification on the Martian surface is critical for understanding the planet's geological history. This paper presents a UNet-based autoencoder model for efficient spectral preprocessing of CRISM MTRDR hyperspectral data, addressing the limitations of traditional methods that are computationally intensive and time-consuming. The proposed model automates key preprocessing steps, such as smoothing and continuum removal, while preserving essential mineral absorption features. Trained on augmented spectra from the MICA spectral library, the model introduces realistic variability to simulate MTRDR data conditions. By integrating this framework, preprocessing time for an 800x800 MTRDR scene is reduced from 1.5 hours to just 5 minutes on an NVIDIA T1600 GPU. The preprocessed spectra are subsequently classified using MICAnet, a deep learning model for Martian mineral identification. Evaluation on labeled CRISM TRDR data demonstrates that the proposed approach achieves competitive accuracy while significantly enhancing preprocessing efficiency. This work highlights the potential of the UNet-based preprocessing framework to improve the speed and reliability of mineral mapping on Mars.

cs.CV↗

arXiv2025

Quality Concerns Caused by Quality Control -- deformation of silicon strip detector modules in thermal cycling tests

The ATLAS experiment at the Large Hadron Collider (LHC) is currently preparing to replace its present Inner Detector (ID) with the upgraded, all-silicon Inner Tracker (ITk) for its High-Luminosity upgrade (HL-LHC). The ITk will consist of a central pixel tracker and the outer strip tracker, consisting of about 19,000 strip detector modules. Each strip module is assembled from up to two sensors, and up to five flexes (depending on its geometry) in a series of gluing, wirebonding and quality control steps. During detector operation, modules will be cooled down to temperatures of about -35C (corresponding to the temperature of the support structures on which they will be mounted) after being initially assembled and stored at room temperature. In order to ensure compatibility with the detector's operating temperature range, modules are subjected to thermal cycling as part of their quality control process. Ten cycles between -35C and +40C are performed for each module, with full electrical characterisation tests at each high and low temperature point. As part of an investigation into the stress experienced by modules during cooling, it was observed that modules generally showed a change in module shape before and after thermal cycling. This paper presents a summary of the discovery and understanding of the observed changes, connecting them with excess module stress, as well as the resulting modifications to the module thermal cycling procedure.

hep-ex↗

arXiv2024

Conic sections in ferroelectric nematics: experiments and mathematical modeling

Domain structure of a fluid ferroelectric nematic is dramatically different from the domain structure of solid ferroelectrics since it is not restricted by rectilinear crystallographic axes and planar surface facets. We demonstrate that thin films of a ferroelectric nematic seeded by colloidal inclusions produce domain walls in the shape of conics such as a parabola. These conics reduce the bound charge within the domains and at the domain walls. An adequate description of the domain structures requires one to analyze the electrostatic energy, which is a challenging task. Instead, we demonstrate that a good approximation to the experimentally observed polydomain textures is obtained when the divergence of spontaneous polarization - which causes the bound charge is heavily penalized by assuming that the elastic constant of splay in the Oseen-Frank energy is much larger than those for twist and bend. The model takes advantage of the fact that the polarization vector is essentially parallel to the nematic director throughout the sample.

cond-mat.soft↗

arXiv2024

Weighted Sum of Segmented Correlation: An Efficient Method for Spectra Matching in Hyperspectral Images

Matching a target spectrum with known spectra in a spectral library is a common method for material identification in hyperspectral imaging research. Hyperspectral spectra exhibit precise absorption features across different wavelength segments, and the unique shapes and positions of these absorptions create distinct spectral signatures for each material, aiding in their identification. Therefore, only the specific positions can be considered for material identification. This study introduces the Weighted Sum of Segmented Correlation method, which calculates correlation indices between various segments of a library and a test spectrum, and derives a matching index, favoring positive correlations and penalizing negative correlations using assigned weights. The effectiveness of this approach is evaluated for mineral identification in hyperspectral images from both Earth and Martian surfaces.

cs.CV↗

arXiv2024

Chiral ground states of ferroelectric liquid crystals

Ferroelectric nematic liquid crystals are formed by achiral molecules with large dipole moments. Its three-dimensional orientational order is universally described as unidirectionally polar. We demonstrate that the ground state of ferroelectric nematic unconstrained by externally imposed alignment directions is chiral, with left- and right-hand twists of polarization. Although the helicoidal deformations and defect walls separating domains of opposite handedness increase the elastic energy, the twists reduce the electrostatic energy and become weaker when the material is doped with ions. The study shows that the polar orientational order of molecules could trigger chirality in the soft matter with no chemically induced chiral centers.

cond-mat.soft↗

arXiv2023

Ferroelectric nematic liquids with conics

Spontaneous electric polarization of solid ferroelectrics follows aligning directions of crystallographic axes. Domains of differently oriented polarization are separated by domain walls (DWs), which are predominantly flat and run along directions dictated by the bulk translational order and the sample surfaces. Here we explore DWs in a ferroelectric nematic (NF) liquid crystal, which is a fluid with polar long-range orientational order but no crystallographic axes nor facets. We demonstrate that DWs in the absence of bulk and surface aligning axes are shaped as conic sections. The conics bisect the angle between two neighboring polarization fields to avoid electric charges. The remarkable bisecting properties of conic sections, known for millennia, play a central role as intrinsic features of liquid ferroelectrics. The findings could be helpful in designing patterns of electric polarization and space charge.

cond-mat.soft↗

arXiv2022

Soliton walls paired by polar surface interactions in a ferroelectric nematic liquid crystal

Surface interactions are responsible for many properties of condensed matter, ranging from crystal faceting to the kinetics of phase transitions. Usually, these interactions are polar along the normal to the interface and apolar within the interface. Here, we demonstrate that polar in-plane surface interactions of a ferroelectric nematic NF produce polar monodomains in micron-thin planar cells and stripes of an alternating electric polarization, separated by 180 degree domain walls, in thicker slabs. The surface polarity binds together pairs of these walls, yielding a total polarization rotation by 360 degrees. The polar contribution to the total surface anchoring strength is on the order of 10%. The domain walls involve splay, bend, and twist of the polarization. The structure suggests that the splay elastic constant is larger than the bend modulus. The 360 degree pairs resemble domain walls in cosmology models with biased vacuums and ferromagnets in an external magnetic field.

cond-mat.soft↗

arXiv2020

Algebraic Methods in Difference Sets and Bent Functions

We provide some applications of a polynomial criterion for difference sets. These include counting the difference sets with specified parameters in terms of Hilbert functions, in particular a count of bent functions. We also consider the question about the bentness of certain Boolean functions introduced by Carlet when the $\mathcal{C}$-condition introduced by him doesn't hold.

math.CO↗

arXiv2020

Improved-RPC for the CMS muon system upgrade for the HL-LHC

During Phase-2 of the LHC, known as the High Luminosity LHC (HL-LHC), the accelerator will increase its instantaneous luminosity to 5 $\times$ 10$^{34}$ cm$^{-2}$ s$^{-1}$, delivering an integrated luminosity of 3000 fb$^{-1}$ over 10 years of operation starting from 2027. In view of the HL-LHC, the CMS muon system will be upgraded to sustain efficient muon triggering and reconstruction performance. Resistive Plate Chambers (RPCs) serve as dedicated detectors for muon triggering due to their excellent timing resolution, and will extend $|η|$ (pseudorapidity) up to a region of 2.4. Before Long Shutdown 3 (LS3), the RE3/1 and RE4/1 stations of the endcap will be equipped with new improved Resistive Plate Chambers (iRPCs) having different design and geometry than the present RPC system. The iRPC geometry configuration improves the detector's rate capability and its ability to survive the harsh background conditions of the HL-LHC. Also, new electronics equipped with excellent timing precision measurements with a resolution of less than 150 ps are developed to readout the RPC detectors from both sides of the strips to allow for good spatial resolution along them. The performance of the iRPC has been studied with gamma radiation at the Gamma Irradiation Facility (GIF++) at CERN. Ongoing longevity studies will help to certify the iRPCs for the HL-LHC running period. The main detector parameters such as the currents, rate and resistivity are regularly monitored as a function of the integrated charge. Preliminary results of the detector performance will be presented.

physics.ins-det↗

arXiv2018

Polynomial Criterion for Abelian Difference Sets

Difference sets are subsets of a group satisfying certain combinatorial property with respect to the group operation. They can be characterized using an equality in the group ring of the corresponding group. In this paper, we exploit the special structure of the group ring of an abelian group to establish a one-to one correspondence of the class of difference sets with specific parameters in that group with the set of all complex solutions of a specified system of polynomial equations. The correspondence also develops some tests for a Boolean function to be a bent function.

math.CO↗