Singular value thresholding two-stage matrix completion for drug sensitivity discovery.

Incomplete data presents significant challenges in drug sensitivity analysis, especially in critical areas like oncology, where precision is paramount. Our study introduces an innovative imputation method designed specifically for low-rank matrices, addressing the crucial challenge of data completion in anticancer drug sensitivity testing. Our method unfolds in two main stages: Initially, the singular value thresholding algorithm is employed for preliminary matrix completion, establishing a solid foundation for subsequent steps. Then, the matrix rows are segmented into distinct blocks based on hierarchical clustering of correlation coefficients, applying singular value thresholding to the largest block, which has been proved to possess the largest entropy. This is followed by a refined data restoration process, where the reconstructed largest block is integrated into the initial matrix completion to achieve the final matrix completion. Compared to other methods, our approach not only improves the accuracy of data restoration but also ensures the integrity and reliability of the imputed values, establishing it as a robust tool for future drug sensitivity analysis.

Corrugated epitaxial graphene/SiC interfaces: photon excitation and probing.

Localized energy exchange and mechanical coupling across a few nm gap at a corrugated graphene-substrate interface remain great challenges to study. In this work, an infrared laser is used to excite an unconstrained epitaxial graphene/SiC interface to induce a local thermal non-equilibrium. The interface behavior is uncovered using a second laser beam for Raman excitation. Using Raman peaks for dual thermal probing, the temperature difference across a gap of just a few nm is determined precisely. The interfacial thermal conductance is found to be extremely low: 410 ± 7 W m(-2) K(-1), indicating poor phonon transport across the interface. By decoupling of the graphene's mechanical and thermal behavior from the Raman wavenumber, the stress in graphene is found to be extremely low, uncovering its flexible mechanical behavior. Based on interface-enhanced Raman, it is found that the increment of interface separation between graphene and SiC can be as large as 2.9 nm when the local thermal equilibrium is destroyed.

Thermally induced increase in energy transport capacity of silkworm silks.

This work reports on the first study of thermally induced effect on energy transport in single filaments of silkworm (Bombyx mori) fibroin degummed mild (type 1), moderate (type 2), to strong (type 3). After heat treatment from 140 to 220°C, the thermal diffusivity of silk fibroin type 1, 2, and 3 increases up to 37.9, 20.9, and 21.5%, respectively. Our detailed scanning electron microscopy study confirms that the sample diameter change is almost negligible before and after heat treatment. Raman analysis is performed on the original and heat-treated (at 147°C) samples. After heat treatment at 147°C, the Raman peaks at 1081, 1230, and 1665 cm(-1) become stronger and narrower, indicating structural transformation from amorphous to crystalline. A structure model composed of amorphous, crystalline, and laterally ordered regions is proposed to explain the structural change by heat treatment. Owing to the close packing of more adjacent laterally ordered regions, the number and size of the crystalline regions of Bombyx mori silk fibroin increase by heat treatment. This structure change gives the observed significant thermal diffusivity increase by heat treatment.

Characterization of Thermal Transport in One-dimensional Solid Materials.

The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials, including conductive, semi-conductive or nonconductive one-dimensional structures. This technique broadens the measurement scope of materials (conductive and nonconductive) and improves the accuracy and stability. If the sample (especially biomaterials, such as human head hair, spider silk, and silkworm silk) is not conductive, it will be coated with a gold layer to make it electronically conductive. The effect of parasitic conduction and radiative losses on the thermal diffusivity can be subtracted during data processing. Then the real thermal conductivity can be calculated with the given value of volume-based specific heat (ρcp), which can be obtained from calibration, noncontact photo-thermal technique or measuring the density and specific heat separately. In this work, human head hair samples are used to show how to set up the experiment, process the experimental data, and subtract the effect of parasitic conduction and radiative losses.

Five orders of magnitude reduction in energy coupling across corrugated graphene/substrate interfaces.

A normal full-contact graphene/substrate interface has been reported to have a thermal conductance in the order of 10(8) Wm(-2)K(-1). The reported work used a sandwiched structure to probe the interface energy coupling, and the phonon behavior in graphene was significantly altered in an undesirable way. Here, we report an intriguing study of energy coupling across unconstrained graphene/substrate interfaces. Using novel Raman-based dual thermal probing, we directly measured the temperature drop across the few nm gap interface that is subjected to a local heat flow induced by a second laser beam heating. The thermal conductance (Gt) for graphene/Si and graphene/SiO2 interfaces is determined as 183 ± 10 and 266 ± 10 Wm(-2)K(-1). At the graphene/Si interface, Gt is 5 orders of magnitude smaller than that of full interface contact. It reveals the remarkable effect of graphene corrugation on interface energy coupling. The measurement result is elucidated by atomistic modeling of local corrugation and energy exchange. By decoupling of graphene's thermal and mechanical behavior, we obtained the stress-induced Raman shift of graphene at around 0.1 cm(-1) or less, suggesting extremely loose interface mechanical coupling. The interface gap variation is evaluated quantitatively on the basis of corrugation-induced Raman enhancement. The interface gap could change as much as 1.8 nm when the local thermal equilibrium is destroyed.

Thermal probing in single microparticle and microfiber induced near-field laser focusing.

Microparticle and microfiber induced near-field laser heating has been widely used in surface nanostructuring. Information about the temperature and stress fields in the nanoscale near-field heating region is imperative for process control and optimization. Probing of this nanoscale temperature, stress, and optical fields remains a great challenge since the heating area is very small (~100 nm or less) and not immediately accessible for sensing. In this work, thermal probing of a single microparticle and microfiber induced near-field focusing on a substrate with laser light is conducted experimentally and interpreted by high-fidelity simulations. The laser (λ = 532 nm) serves as both heating and Raman probing sources. It is very interesting to note that variation of the Raman intensity, wavenumber, and linewidth all can be used to precisely capture the size of the micro-size subject on the substrate. Nanoscale mapping of conjugated optical, thermal, and stress effects, and the de-conjugation of these effects are performed. The effect of the laser fluence on the temperature and stress in the nanoscale heating region is investigated. With laser fluence of 3.9 ×10(9) W/m(2) and for a 1.21 µm silica particle induced laser heating, the maximum temperature rise and local stress are 58.5 K and 160 MPa, respectively. For a 6.24 µm glass fiber, they are 33.0 K and 120 MPa, respectively. Experimental results are explained and consistent with three-dimensional high-fidelity optical, thermal and stress field simulation.

Nanoscale probing of thermal, stress, and optical fields under near-field laser heating.

Micro/nanoparticle induced near-field laser ultra-focusing and heating has been widely used in laser-assisted nanopatterning and nanolithography to pattern nanoscale features on a large-area substrate. Knowledge of the temperature and stress in the nanoscale near-field heating region is critical for process control and optimization. At present, probing of the nanoscale temperature, stress, and optical fields remains a great challenge since the heating area is very small (~100 nm or less) and not immediately accessible for sensing. In this work, we report the first experimental study on nanoscale mapping of particle-induced thermal, stress, and optical fields by using a single laser for both near-field excitation and Raman probing. The mapping results based on Raman intensity variation, wavenumber shift, and linewidth broadening all give consistent conjugated thermal, stress, and near-field focusing effects at a 20 nm resolution (<λ/26, λ = 32 nm). Nanoscale mapping of near-field effects of particles from 1210 down to 160 nm demonstrates the strong capacity of such a technique. By developing a new strategy for physical analysis, we have de-conjugated the effects of temperature, stress, and near-field focusing from the Raman mapping. The temperature rise and stress in the nanoscale heating region is evaluated at different energy levels. High-fidelity electromagnetic and temperature field simulation is conducted to accurately interpret the experimental results.

Sub-wavelength temperature probing in near-field laser heating by particles.

This work reports on the first time experimental investigation of temperature field inside silicon substrates under particle-induced near-field focusing at a sub-wavelength resolution. The noncontact Raman thermometry technique employing both Raman shift and full width at half maximum (FWHM) methods is employed to investigate the temperature rise in silicon beneath silica particles. Silica particles of three diameters (400, 800 and 1210 nm), each under four laser energy fluxes of 2.5 × 10(8), 3.8 ×10(8), 6.9 ×10(8) and 8.6 ×10(8) W/m(2), are used to investigate the effects of particle size and laser energy flux. The experimental results indicate that as the particle size or the laser energy flux increases, the temperature rise inside the substrate goes higher. Maximum temperature rises of 55.8 K (based on Raman FWHM method) and 29.3K (based on Raman shift method) are observed inside the silicon under particles of 1210 nm diameter with an incident laser of 8.6 × 10(8) W/m(2). The difference is largely due to the stress inside the silicon caused by the laser heating. To explore the mechanism of heating at the sub-wavelength scale, high-fidelity simulations are conducted on the enhanced electric and temperature fields. Modeling results agree with experiment qualitatively, and discussions are provided about the reasons for their discrepancy.