A croconic acid-derived narrow band gap conjugated microporous polymer

Croconic acid, a novel highly electron-deficient building block, was introduced into a conjugated microporous polymer (CTPA). The CMP possesses strong donor-acceptor interactions, which resulted in near-IR absorption (red edge ∼1350 nm), a narrow bandgap (<1 eV) and high electrical conductivity upon doping (0.1 S m^-1). Compared to the squaric acid congener (STPA), CTPA showed superior optical, electronic and electrical properties.

Learning from perpetrator replacement to remove crime opportunities and prevent poaching of the Sundarbans tiger

Illegal wildlife trade (IWT) is one of the leading causes of the decline in high-value species. Crime-reduction strategies to counter IWT can have unintended effects, with crime displacement occurring when offenders react to such interventions. Despite the value of understanding how and why displacement occurs for informing conservation strategies, few examples are published. We explored a case of perpetrator replacement following an intervention and drew lessons for conservation strategies for high-value species. Poaching and subsequent trade threaten the Sundarbans tiger (Panthera tigris). Pirate gangs were the dominant poachers from 1980 to 2017, but following an extensive campaign, the Sundarbans was declared pirate free in 2018. We interviewed 280 individuals, including 100 tiger poachers, from 26 administrative unions bordering the Sundarbans and used interviewee responses to compare the poaching situation during and after the pirate era. We analyzed the spatial distribution of tiger poachers among the unions and used crime script analysis of the dominant poacher type to identify intervention. Because pirates opportunistically poached tigers, the government's successful counter-pirate campaign inadvertently removed the dominant tiger poaching type. However, a temporary reduction in poaching was rapidly cancelled out by the emergence of at least 32 specialist tiger-poaching teams. With the risk of extortion and robbery from pirates gone, other groups increased the frequency of opportunistic and targeted tiger poaching. Based on expert interviews, we estimated that 341 tiger poachers of all types are active throughout the unions, with 79% of specialists concentrated in 27% of unions. The highly focused counter-pirate campaign reduced motivations and opportunities for piracy but left intact the opportunity structure and trade connections for tiger poaching, and with insufficient enforcement officers trading has flourished. Interventions targeting opportunities for poaching by specialist tiger poachers include heightened surveillance and reporting mechanisms and alternative livelihood provision to disincentivize poaching.

Mimicking Electromagnetic Wave Coupling in Tokamak Plasma with Fishnet Metamaterials

This paper reports a fishnet hyperbolic metamaterial that mimics the electromagnetic properties of magnetically confined plasma. These electromagnetic properties are strongly anisotropic and different from any conventional material, therefore cannot be mimicked by bulk materials. The structure is made of a stack of thin copper grids spaced by Rohacell foam. We numerically and experimentally show that this kind of structuration matches well the properties of a homogeneous plasma. This solution breaks a long-lasting bottleneck and will accelerate the development of high-frequency heating systems to be used in nuclear fusion.

Wavelength-scale light concentrator made by direct 3D laser writing of polymer metamaterials

We report on the realization of functional infrared light concentrators based on a thick layer of air-polymer metamaterial with controlled pore size gradients. The design features an optimum gradient index profile leading to light focusing in the Fresnel zone of the structures for two selected operating wavelength domains near 5.6 and 10.4 μm. The metamaterial which consists in a thick polymer containing air holes with diameters ranging from λ/20 to λ/8 is made using a 3D lithography technique based on the two-photon polymerization of a homemade photopolymer. Infrared imaging of the structures reveals a tight focusing for both structures with a maximum local intensity increase by a factor of 2.5 for a concentrator volume of 1.5 λ³, slightly limited by the residual absorption of the selected polymer. Such porous and flat metamaterial structures offer interesting perspectives to increase infrared detector performance at the pixel level for imaging or sensing applications.

Value of wound biopsy in chronic venous ulceration

Objectives: Malignant transformation in chronic venous ulcers (CVU) is a limb threatening complication, which has an insidious onset. Clinical experience in our practice suggests a lack of suspicious macroscopic features making diagnosis difficult. The aim of this study is to evaluate the role of routine wound biopsy in the outpatient clinic for CVU without suspicious appearances but with no signs of healing despite appropriate treatment.

Methods: A three-year (2000-2003) retrospective review of records for all patients who underwent biopsy of a CVU in the outpatient clinic in a specialist wound healing clinic set in a university hospital.

Results: In our series ( n =76), three indications for biopsy were identified: CVU that had developed features suspicious of carcinoma ( n =17), CVU that had no suspicious features but were non-healing ( n =24) and CVU that had developed features of inflammatory ulceration ( n =35). A positive finding of carcinoma (squamous or basal cell carcinoma) or intraepidermal carcinoma (Bowen's disease) was made in four (24%), nine (37.5%) and 0 cases respectively.

Conclusions: Malignancy may arise in CVU without showing suspicious features and wound biopsy should be advocated for any ulcer that fails to respond to appropriate treatment.

Time-driven superoscillations with negative refraction

The flat-lens concept based on negative refraction proposed by Veselago in 1968 has been mostly investigated in the monochromatic regime. It was recently recognized that time development of the superlensing effect discovered in 2000 by Pendry is yet to be assessed and may spring surprises: Time-dependent illumination could improve the spatial resolution of the focusing. We investigate dynamics of flexural wave focusing by a 45°-tilted square lattice of circular holes drilled in a duralumin plate. Time-resolved experiments reveal that the focused image shrinks with time below the diffraction limit, with a lateral resolution increasing from 0.8λ to 0.35λ, whereas focusing under harmonic excitation remains diffraction limited. Modal analysis reveals the role in pulse reconstruction of radiating lens resonances, which repeatedly self-synchronize at the focal spot to shape a superoscillating field.

Scattering by complex inhomogeneous objects: a first-order reciprocity method

The scattering by slightly inhomogeneous objects has been studied by a first-order method and reciprocity theorem. The scattering calculation reported in this manuscript is based on a simple computation of the field in a defectless structure at different incidence angles. The numerical results have been compared to those given by an exact calculation. It is shown that the method enables to handle complex structures with an affordable computational burden. A major advantage of the method is its ability to treat different defects without recomputing the field, i.e, the main part of the computation time. In addition, for defects in periodic structures, the field computation can be limited to a single period thus leading to an important decrease of the computational time and required memory. This method is believed to provide significant advantages for the engineering of optical devices.

Sun protection and hydration of stratum corneum: a study by 2-D differential method

OBJECTIVE

The stratum corneum is the outermost layer of the skin. Its components and its morphology (such as the size of its cells) play a role in sun protection, and it has been noted that the stratum corneum hydration can change these properties. Sunscreens, applied on the skin, can be more or less effective depending on the stratum corneum characteristics. We therefore propose to simulate the quality of the sun protection and the effect of the stratum corneum hydration on the sun protection.

METHODS

We first determined the sunscreen distribution on a plastic substrate using an optical coherence tomography device. We were then able to calculate, by 2-D differential method, the extinction of several sunscreens. We modelled the hydration of the stratum corneum, by changing the substrate with corneocytes of different thicknesses.

RESULTS

Our results showed that hydrated stratum corneum protects more against the UV. The benefit from changing the substrate varies depending on the sunscreen applied.

CONCLUSION

We modelled sunscreens on different substrates using electromagnetic simulations. To compare these results with measurements, we have to carefully hydrate or dehydrate the SC: the simulations did not take into account modifications of the surface (water on the surface for example) or any change in the characteristics of the stratum corneum other than the modification of the corneocytes thickness.

Platonic scattering cancellation for bending waves in a thin plate

We propose an ultra-thin elastic cloak to control the scattering of bending waves in isotropic heterogeneous thin plates. The cloak design makes use of the scattering cancellation technique applied, for the first time, to the biharmonic operator describing the propagation of bending waves in thin plates. We first analyze scattering from hard and soft cylindrical objects in the quasistatic limit, then we prove that the scattering of bending waves from an object in the near and far-field regions can be suppressed significantly by covering it with a suitably designed coating. Beyond camouflaging, these findings may have potential applications in protection of buildings from earthquakes and isolating structures from vibrations in the motor vehicle industry.

Experiments on seismic metamaterials: molding surface waves

Materials engineered at the micro- and nanometer scales have had a tremendous and lasting impact in photonics and phononics. At much larger scales, natural soils civil engineered at decimeter to meter scales may interact with seismic waves when the global properties of the medium are modified, or alternatively thanks to a seismic metamaterial constituted of a mesh of vertical empty inclusions bored in the initial soil. Here, we show the experimental results of a seismic test carried out using seismic waves generated by a monochromatic vibrocompaction probe. Measurements of the particles' velocities show a modification of the seismic energy distribution in the presence of the metamaterial in agreement with numerical simulations using an approximate plate model. For complex natural materials such as soils, this large-scale experiment was needed to show the practical feasibility of seismic metamaterials and to stress their importance for applications in civil engineering. We anticipate this experiment to be a starting point for smart devices for anthropic and natural vibrations.

Surface and bulk scattering by magnetic and dielectric inhomogeneities: a first-order method

The scattering of a magnetodielectric multilayer has been studied by a first-order method. The model reported in this manuscript relies on the equivalence between heterogeneities of the medium and fictitious electric and magnetic sources. Types of inhomogeneities considered are roughness and bulk inhomogeneities and concern both permittivity and permeability. The numerical results are compared to those given in previous papers for optical scattering. It is shown in the microwave spectra that angle-resolved scattering allows identification of the scattering origins (permittivity or permeability spectra). The cases of isotropic films and metamaterials are presented and discussed.

Plasmon assisted thermal modulation in nanoparticles

Single-particle interactions hold the promise of nanometer-scale devices in areas such as data communications and storage, nanolithography, waveguides, renewable energy and therapeutics. We propose that the collective electronic properties possessed by noble metal nanoparticles may be exploited for device actuation via the unapparent mechanism of plasmon-assisted heat generation and flux. The temperature dependence of the dielectric function and the thermal transport properties of the particles play the central role in the feasibility of the thermally-actuated system, however the behavior of these thermoplasmonic processes is unclear. We experimentally and computationally analyzed modulation via thermoplasmonic processes on a test system of gold (Au) nano-islands. Modulation and energy transport in discontinuous domains exhibited quantitatively different characteristics compared to thin films. The results have implications for all surface plasmon based nano-devices where inevitable small-scale thermal processes are present.

‘Young’ Oral Fibroblasts Are Geno/Phenotypically Distinct

Wound healing within the oral mucosa results in minimal scar formation compared with wounds within the skin. We have recently demonstrated distinct differences in the aging profiles of cells (oral mucosal and patient-matched skin fibroblasts) isolated from these tissues. We hypothesized that the increased replicative potential of oral mucosal fibroblasts may confer upon them preferential wound-healing capacities. Passage-matched early cultures of oral mucosal fibroblasts and skin fibroblasts demonstrated distinct gene expression profiles, with several genes linked to wound healing/tissue repair. This was related to an increased ability of the ‘replicatively younger’ oral mucosal fibroblasts to repopulate a wound space and reorganize their surrounding extracellular matrix environment, key activities during the wound-healing process. We conclude that oral mucosal fibroblasts exhibit a preferential healing response in vivo, due to their ‘replicatively younger’ phenotype when compared with that of patient-matched skin fibroblasts.

Negative refraction, surface modes, and superlensing effect via homogenization near resonances for a finite array of split-ring resonators

We present a theoretical and numerical analysis of liquid surface waves (LSWs) localized at the boundary of a phononic crystal consisting of split-ring resonators (SRRs). We first derive the homogenized parameters of the fluid-filled structure using a three-scale asymptotic expansion in the linearized Navier-Stokes equations. In the limit when the wavelength of the LSW is much larger than the typical heterogeneity size of the phononic crystal, we show that it behaves as an artificial fluid with an anisotropic effective shear modulus and a dispersive effective-mass density. We then analyze dispersion diagrams associated with LSW propagating within an infinite array of SRR, for which eigensolutions are sought in the form of Floquet-Bloch waves. The main emphasis is given to the study of localized modes within such a periodic fluid-filled structure and to the control of low-frequency stop bands associated with resonances of SRRs. Considering a macrocell, we are able to compute the dispersion of LSW supported by a semi-infinite phononic crystal of SRRs. We find that the dispersion of this evanescent mode nearly sits within the first stop band of the doubly periodic structure. We further discover that it is linked to the frequency at which the effective-mass density of the homogenized phononic crystal becomes negative. We demonstrate that this surface mode displays the hallmarks of all-angle negative refraction and it leads to a superlensing effect. Last, we note that our homogenization results for the velocity potential can be applied mutatis mutandis to designs of electromagnetic and acoustic superlenses for transverse electric waves propagating in arrays of infinite conducting SRRs and antiplane shear waves in arrays of cracks shaped as SRRs.

Increased Oral Fibroblast Lifespan Is Telomerase-independent

Oral mucosal wound-healing is characterized by rapid re-epithelialization and remodeling, with minimal scar formation. This may be attributed to the distinct phenotypic characteristics of the resident fibroblasts. To test this hypothesis, we investigated patient-matched oral mucosal and skin fibroblasts. Compared with skin fibroblasts, oral mucosal fibroblasts had longer proliferative lifespans, underwent more population doublings, and experienced senescence later, which was directly related to longer telomere lengths within oral mucosal fibroblasts. The presence of these longer telomeres was independent of telomerase expression, since both oral oral mucosal fibroblasts and skin fibroblasts were negative for active telomerase, as assessed according to the Telomeric Repeat Amplification Protocol. This study has demonstrated that, compared with skin fibroblasts, oral mucosal fibroblasts are ‘younger’, with a more embryonic/fetal-like phenotype that may provide a notable advantage for their ability to repair wounds in a scarless fashion.

Broadband cylindrical acoustic cloak for linear surface waves in a fluid

We describe the first practical realization of a cylindrical cloak for linear surface liquid waves. This structured metamaterial bends surface waves radiated by a closely located acoustic source over a finite interval of Hertz frequencies. We demonstrate theoretically its unique mechanism using homogenization theory: the cloak behaves as an effective anisotropic fluid characterized by a diagonal stress tensor in a cylindrical basis. A low azimuthal viscosity is achieved, where the fluid flows most rapidly. Numerical simulations demonstrate that the homogenized cloak behaves like the actual structured cloak. We experimentally analyze the decreased backscattering of a fluid with low viscosity and finite density (methoxynonafluorobutane) from a cylindrical rigid obstacle surrounded by the cloak when it is located a couple of wavelengths away from the acoustic source.

Achieving invisibility over a finite range of frequencies

We analyze cloaking of transverse electric (TE) fields through homogenization of radially symmetric metallic structures. The two-dimensional circular cloak consists of concentric layers cut into a large number of small infinitely conducting sectors which is equivalent to a highly anisotropic permittivity. We find that a wave radiated by a magnetic line current source located a couple of wavelengths away from the cloak is almost unperturbed in magnitude but not in phase. Our structured cloak is shown to work for different wavelengths provided they are ten times larger than the outermost sectors.

Analytical and numerical analysis of lensing effect for linear surface water waves through a square array of nearly touching rigid square cylinders

This paper describes transport properties of linear water waves propagating within a square array of fixed square cylinders. The main focus is on achieving the conditions for all-angle-negative-refraction (AANR) thanks to anomalous dispersion in fluid-filled periodic structures. Of particular interest are two limit cases when either the edges or the vertices of the cylinders come close to touching. In the former case, the array can be approximated by a lattice of thin water channels (for which dispersion curves are given in closed form and thus frequencies at which AANR occurs) whereas in the latter case, the array behaves as a checkerboard with cells consisting either of water tanks or rigid cylinders (for which standing modes are given in closed form). The tools of choice for the present analysis are, on the one hand, the finite element method which solves numerically spectral problems in periodic media, and on the other hand, a two-scale asymptotic method which provides estimates of dispersion curves and associated eigenfields through a lattice approximation (namely thin water channels between rigid cylinders). Simple duality correspondences are found based on fourfold symmetry of square water checkerboards that allow us to get some insight into their spectra. Last, some numerical evidence is provided for water waves focusing with no astigmatism through such arrays, when they are of finite extent.

Strong modification of the nonlinear optical response of metallic subwavelength hole arrays

The influence of hole shape on the nonlinear optical properties of metallic subwavelength hole arrays is investigated. It is found that the amount of second harmonics generated can be enhanced by changing the hole shape. In part this increase is a direct result of the effect of hole shape on the linear transmission properties. Remarkably, in addition to enhancements that follow directly from the linear properties of the array, we find a hot hole shape. For rectangular holes the effective nonlinear response is enhanced by more than 1 order of magnitude for one particular aspect ratio. This enhancement can be attributed to slow propagation of the fundamental wavelength through the holes which occurs close to the hole cutoff.

Photonic crystal lens: from negative refraction and negative index to negative permittivity and permeability

We consider a dielectric photonic crystal made of cylindrical holes in a high index matrix. We show that a given finite size photonic crystal can mimic a homogeneous material whose permittivity and permeability are negative. We pay attention to the limitation of the homogeneous medium model and the vital role of the truncation of the crystal.

Automated QSPR through Competitive Workflow

This paper describes a novel software architecture, Competitive Workflow, which implements workflow as a distributed and competitive multi-agent system. The implementation of a competitive workflow architecture designed to model important computer-aided molecular design workflows, the Discovery Bus, is described. QSPR modelling results for three example ADME datasets, for solubility, human plasma protein binding and P-glycoprotein substrates using an autonomous QSPR modelling workflow implemented on the Discovery Bus are presented. The autonomous QSPR system allows exhaustive exploration of descriptor and model space, automated model validation and continuous updating as new data and methods are made available. Prediction of properties of novel structures by an ensemble of models is also a feature of the system.

Band gap formation and multiple scattering in photonic quasicrystals with a Penrose-type lattice

This Letter presents a study of the local density of states (LDOS) in photonic quasicrystals. We show that the LDOS of a Penrose-type quasicrystal exhibits small additional band gaps. Among the band gaps, some exhibit a behavior similar to that typical of photonic crystals, while others do not. The development of certain band gaps requires large-size quasicrystals. It is explained by the long-range interactions involved in their formation. Moreover, the frequencies where the band gaps occur are not necessarily explained using single scattering and should therefore involve multiple scattering.

Informed consent should be obtained from patients to use products (skin substitutes) and dressings containing biological material

BACKGROUND

Biological products (tissue engineered skin, allograft and xenograft, and biological dressings) are widely used in the treatment of burns, chronic wounds, and other forms of acute injury. However, the religious and ethical issues, including consent, arising from their use have never been addressed in the medical literature.

AIMS

This study was aimed to ascertain the views of religious leaders about the acceptability of biological products and to evaluate awareness among healthcare professionals about their constituents.

METHODS

The religious groups that make up about 75% of the United Kingdom population were identified and a questionnaire on 11 biological products was sent to its leaders. Another questionnaire concerning 17 products (11 biological and 6 synthetic dressings) was sent to 100 healthcare professionals working in seven specialist units in the UK.

RESULTS

All religious leaders (100% response rate) replied, some after consultation with international bodies. Among them, 77% said that patients should be informed of the constituents of the biological products and consent obtained. Some leaders expressed concerns about particular products including the transmission of viral and prion diseases, cruelty to animals, and material derived from neonates. None of the healthcare professionals (73% response rate) surveyed knew the constituents of all the products correctly.

CONCLUSION

Ignoring religious sensitivities and neglecting consent in the usage of biological products could have very serious implications, including litigation. Hospitals and manufacturers should take immediate measures to enlighten healthcare professionals of the constituents of these products so that they can obtain informed consent from patients.

Distinct phenotype associated with a cryptic subtelomeric deletion of 19p13.3-pter

Telomeres are gene rich regions with a high recombination rate. Cryptic subtelomeric rearrangements are estimated to account for 5% of mental retardation/malformation syndromes. Here we present the first patient with a deletion of 19p13.3, identified by subtelomeric FISH analysis. His features included a distinctive facial appearance, cleft palate, hearing impairment, congenital heart malformation, keloid scarring, immune dysregulation, and mild learning difficulties. Subtelomeric FISH analysis identified a deletion of 19p13.3-pter. The deletion size was determined to be 1.2 Mb by FISH analysis. It extended from within the chromosomal region covered by BAC RP11-50C6 to 19pter. The deleted area encompassed approximately 60 genes. Fifteen possible candidate genes were considered with respect to the phenotype, including follistatin-related precursor 3 (FSTL3) and serine-threonine kinase 11 (STK-11).

Strong influence of hole shape on extraordinary transmission through periodic arrays of subwavelength holes

We show that extraordinary light transmission of periodic subwavelength hole arrays, generally attributed to surface-plasmon resonances, is strongly influenced by the hole shape. Both experiments and calculations, based on a Fourier modal method, demonstrate that a shape change from circular to rectangular increases the normalized transmission by an order of magnitude while the hole area decreases. Moreover, the spectra exhibit large redshifts (approximately 2500 cm(-1)). A comparison with the transmission of isolated holes shows that shape resonances of the rectangular holes play a dominant role.

Exclusion of deep vein thrombosis by measuring spot skin temperatures using a hand-held thermo-comparator

Objectives: Thermograms have shown that deep vein thrombosis (DVT) causes an increase in temperature in the leg. We have studied for the first time, the viability of measuring spot skin temperatures using a hand-held instrument called a thermo-comparator as an inexpensive, simple and reliable method of excluding the diagnosis of DVT.

Methods: A total of 33 patients with suspected DVT had spot skin temperatures taken on specified areas of each leg using the instrument. The results were compared with duplex scans of the patient and with venography in some patients.

Results: There was a mean temperature gradient of 3.38°C down each normal leg. All 10 patients with DVT confirmed by duplex scan or venogram also had raised temperatures compared with surrounding areas, without the normal temperature gradient down the leg (true positive, 100%). This instrument did not have any false negatives and achieved 100% sensitivity and 100% negative predictive value.

Conclusions: The thermo-comparator excluded a diagnosis of DVT in 39% of patients and has the potential for use in primary care as a screening tool to reduce the number of patients sent to hospital unnecessarily.

Thromboprophylaxis can be omitted in selected patients undergoing varicose vein surgery and hernia repair

BACKGROUND

There is no current agreement on the routine use of thromboprophylaxis in patients undergoing varicose vein surgery and hernia repair. In the authors' hospital, prophylaxis is given only to those considered to be at an increased risk. A retrospective review was conducted to determine whether it was safe to omit prophylaxis in low-risk patients.

METHODS

Data were extracted from the hospital database about all patients who underwent the above procedures between January 1997 and December 2001. The case notes of patients who developed venous thromboembolism (VTE) within 3 months of surgery were reviewed. The pharmacy database was then analysed to determine the effect of prophylaxis.

RESULTS

A total of 4670 patients were identified. Some 2186 patients had varicose vein surgery; 1283 patients received prophylaxis, of whom four developed VTE. None of the 903 patients who did not receive prophylaxis developed VTE. A total of 2484 patients had hernia repair, of whom 1854 patients received prophylaxis and 630 did not; one patient from each group developed VTE.

CONCLUSION

Low-risk patients having hernia and vein surgery do not need thromboprophylaxis.

Morpho butterflies wings color modeled with lamellar grating theory

We describe an approach for converting reflection coefficients of any structure into colors, taking into account human color perception. This procedure is applied to the study of the colors reflected by Morpho rhetenor butterflies wings. The scales of these wings have a tree-like periodic structure which is modeled with the help of a rigorous lamellar grating electromagnetic theory. In this way, we are able to determine the colors reflected by the wing under various illumination conditions.

Anomalous refractive properties of photonic crystals

We describe methods of investigating the behavior of photonic crystals. Our approach establishes a link between the dispersion relation of the Bloch modes for an infinite crystal (which describes the intrinsic properties of the photonic crystal in the absence of an incident field) and the diffraction problem of a grating (finite photonic crystal) illuminated by an incident field. We point out the relationship between the translation operator of the first problem and the transfer matrix of the second. The eigenvalues of the transfer matrix contain information about the dispersion relation. This approach enables us to answer questions such as When does ultrarefraction occur? Can the photonic crystal simulate a homogeneous and isotropic material with low effective index? This approach also enables us to determine suitable parameters to obtain ultrarefractive or negative refraction properties and to design optical devices such as highly dispersive microprisms and ultrarefractive microlenses. Rigorous computations add a quantitative aspect and demonstrate the relevance of our approach.

Second-harmonic specular and scattered generated light: application to the experimental study of zinc-sulfide thin films

We present measurements of second-harmonic generation with zinc-sulfide thin films. Both scattered light and specular light are investigated in linear optics as well as in second-harmonic generation. We show that second-harmonic generation is a powerful tool for understanding the nonlinear properties of thin films; it allows the study of the anisotropy found in the scattered and specular second harmonic. Using the symmetry of susceptibility tensors, we show that the films cannot be considered homogeneous when the crystallites are large. Finally, we outline nonlinear scattering measurements, which bring out the usefulness of second-harmonic light in probing the structure of thin films.