Structured near-infrared Magnetic Circular Dichroism spectra of the Mn4CaO5 cluster of PSII in T. vulcanus are dominated by Mn(IV) d-d ‘spin-flip’ transitions

Photosystem II passes through four metastable S-states in catalysing light-driven water oxidation. Variable temperature variable field (VTVH) Magnetic Circular Dichroism (MCD) spectra in PSII of Thermosynochococcus (T.) vulcanus for each S-state are reported. These spectra, along with assignments, provide a new window into the electronic and magnetic structure of Mn₄CaO₅. VTVH MCD spectra taken in the S₂ state provide a clear g = 2, S = 1/2 paramagnetic characteristic, which is entirely consistent with that known by EPR. The three features, seen as positive (+) at 749 nm, negative (?) at 773 nm and (+) at 808 nm are assigned as ⁴A → ²E spin-flips within the d³ configuration of the Mn(IV) centres present. This assignment is supported by comparison(s) to spin-flips seen in a range of Mn(IV) materials. S₃ exhibits a more intense (?) MCD peak at 764 nm and has a stronger MCD saturation characteristic. This S₃ MCD saturation behaviour can be accurately modelled using parameters taken directly from analyses of EPR spectra. We see no evidence for Mn(III) d-d absorption in the near-IR of any S-state. We suggest that Mn(IV)-based absorption may be responsible for the well-known near-IR induced changes induced in S₂ EPR spectra of T. vulcanus and not Mn(III)-based, as has been commonly assumed. Through an analysis of the nephelauxetic effect, the excitation energy of S-state dependent spin-flips seen may help identify coordination characteristics and changes at each Mn(IV). A prospectus as to what more detailed S-state dependent MCD studies promise to achieve is outlined.     

Ferromagnetic exchange coupling in the linear,chloride-bridged cluster (cyclam)CoII[(μ-Cl)UIV(Me2Pz)4]2

The trinuclear cluster (cyclam)Co[(μ-Cl)U(Me₂Pz)₄]₂ (cyclam = 1,4,8,11-tetraazacyclotetradecane, Me₂Pz^? = 3,5-dimethylpyrazolate) is synthesized through cleavage of the homoleptic dimer [U(Me₂Pz)₄]₂ by (cyclam)CoCl₂. A single crystal X-ray diffraction analysis reveals a linear chloride-bridged structure analogous to that previously reported for (cyclam)M[(μ-Cl)U(Me₂Pz)₄]₂ (M = Ni, Cu, Zn). The magnetic exchange coupling of the CoU₂ cluster was probed by analyzing the temperature dependence of its magnetic susceptibility. Comparison of χ_MT versus T between the CoU₂ species and the diamagnetic ZnU₂ cluster demonstrates the presence of ferromagnetic coupling between the Co^II and U^IV centers. We present methods for estimating upper and lower bounds for the exchange interaction energy in such systems and find that for CoU₂, the exchange constant, J, lies in the range 15–48 cm^?1. Application of these methods to the previously reported NiU₂ cluster suggests somewhat weaker ferromagnetic exchange, with J lying in the range 2.8–19 cm^?1. AC magnetic susceptibility experiments were not indicative of single-molecule magnet behavior for the CoU₂ cluster, although qualitative interpretation of the low-temperature magnetization data suggests the presence of significant zero-field splitting in the ground state.     

Chitosan-functionalized poly(methyl methacrylate) particles by spinning disk processing for lipase immobilization

Chitosan-functionalized poly(methyl methacrylate) (PMMA-CH) particles were prepared by complexation between the negatively charged PMMA particles and the positively charged chitosan via a spinning disk processing. Processing parameters; feed rate and spinning speed, were optimized, which were traced by size distribution profiles of the formed PMMA-CH particles. Their sizes and net surface charges were found to be affected by MWs of chitosan (45, 100, and 230 kDa) used. Microscopic evidences were used to confirm their core–shell morphology. Chemical characteristics and thermal stability of such particles were determined by FTIR and TGA, respectively. Then, their ability to immobilize lipase (EC 3.1.1.3) was conducted and followed through zeta potential measurement. The percentage of lipase adsorption capacity increased with increasing lipase content, but the value decreased when the size of PMMA-CH particles increased. Also, the activity of lipase attached on PMMA-CH particles’ surface was preserved and increased with lipase loading.     

Hydroxy functional acrylate and methacrylate monomers prepared via lipase—catalyzed transacylation reactions

Candida antarctica lipase B (CAL-B, Novozyme 435) catalyzes the transacylation of methyl acrylate and methyl methacrylate with diols and triols in 2-methyl-2-butanol at 50 °C. Under the experimental conditions, up to 70 mol% of the acyl donor methyl acrylate was converted. Methyl methacrylate is the less efficient acyl donor (up to 60 mol%) due to the higher sterical hindrance in the enzymatic transacylation. Under the reaction conditions high yields of the mono-acylated products are obtained, which contain minor amounts of bis(meth)acrylates. In addition it was observed that Novozyme 435 catalyzes regioselectively the acylation of the primary hydroxyl groups. In comparison with the chemical catalyzed route no selectivity was observed for unsubstituted diols. For substituted diols more mono-acylated product was formed in the lipase-catalyzed reaction than in the chemical catalyzed reaction.     

Photoprocesses and magnetic behavior of photochromic transition metal indoline[phenanthrolinospirooxazine] complexes: Tunable photochromic materials

We have synthesized a series of M(IPSO)₃(BPh₄)₂ complexes consisting of first row transition metals and a photochromic phenanthroline ligand: (M = Mn(II), Fe(II), Co(II), Ni(II), Zn(II), and Cu(II), IPSO = spiro[indole-phenanthrolinoxazine]). The optical properties associated with photochromic behavior were evaluated by determination of the (i) equilibrium constants (K) for the thermal and photostationary states, (ii) rates of photochemical ring-opening and ring-closure, and (iii) rates of thermal ring-closure. The photocolorability values associated with conversion from the colorless spirooxazine to the colored photomerocyanine isomer are greatly enhanced upon metal coordination. Variable temperature magnetic susceptibility experiments suggest deviations from cubic symmetry associated with desymmetrization induced by a dependence of ligand field strength on the photochromic state of IPSO.     

The effect of molecular packing on the occurrence of spin crossover phenomena in one-dimensional Fe(II)-bis-Schiff base complexes

Two new one-dimensional Fe(II)-bis-Schiff base complexes, [Fe(L1)(pyz)] · CH₂Cl₂ (1) and [Fe(L2)(pyz)] · 2CH₂Cl₂ (2) (H₂L1 = bis(O-vanillin)-O-phenylenediimine, H₂L2 = bis(O-vanillin)-2,3-naphthalenediimine, pyz = pyrazine) are reported with their crystal structures and magnetic property. Compound 1 shows a two-step SCO behavior while 2 shows HS at all the temperature range measured. Although the extension of aromatic moiety from benzene (L1) to naphthalene (L2) was introduced for the purpose of strengthening the cooperativity, it leads to the absence of SCO, due to the unanticipated π–π interaction, which leads to the longer Fe–N bond lengths and a weak ligand field around Fe(II) ion.     

The concentrations of major and trace elements in rat kidney: Aging effects and mutual relationships

The concentrations of 26 major to trace elements in rat kidneys aging from 5 to 113 weeks old were determined. The rats investigated were the same rats used previously reported to have 29 elements in bones (femurs). The samples were decomposed by high purity nitric acid and hydrogen peroxide. Eight elements (Na, Mg, Si, P, K, Ca, Fe and Zn) were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) and 18 elements (Mn, Co, Ni, Cu, As, Se, Rb, Sr, Mo, Cd, Sn, Sb, Cs, Ba, Tl, Pb, Bi and U) were determined using inductively coupled plasma mass spectrometry (ICP-MS). The aging effects on the concentrations of these elements and mutual elemental relationships were investigated. Analysis of variance (ANOVA) for age variations indicated that the concentrations of P, K, Mn and Mo were almost constant across the age of rats (p > 0.3). The concentration of many elements such as Na, Mg, Ca, Fe, Co, Cu, Zn, As, Se, Cd, Sn, Sb, Tl, Pb and Bi, showed significant increasing trends (p < 0.01) with different patterns. Rubidium, Cs, Pb and Bi showed significant age variations but not monotonic trends. Silicon, Ni, Sr, Ba and U showed large concentration scatterings without any significant trends (p > 0.01). The metabolism of these elements may not be well established in the kidney. Many toxic elements such as As, Cd, Sn, Pb and Bi showed a narrow concentration range among age-matched rats. The kidney may have established metabolic mechanisms to confine or accumulate these toxic elements even though their concentrations are very low (e.g., 10 ng g^?1 of Cd). These elements also closely coupled with Fe. A cluster analysis was performed using an elemental correlation matrix and indicated that these elements, including Fe, formed a cluster. However, another cluster analysis using “an aging effect eliminated” elemental correlation showed different clustering in which the Fe, Cd cluster disappeared.     

Supermacroporous hydrophobic affinity cryogels for protein chromatography

N-Methacryloyl-l-tryptophan (MATrp) containing poly(2-hydroxyethyl methacrylate) based supermacroporous cryogel [PHEMATrp] was prepared for lysozyme purification form chicken egg white. MATrp was synthesized by reacting methacryloyl chloride with l-tryptophan methyl ester and provided hydrophobic functionality to the cryogel. PHEMATrp cryogel with 60–100 μm pore size was obtained by free radical polymerization of HEMA and MATrp having a specific surface area of 50 m²/g. PHEMATrp cryogel was characterized by swelling studies, FTIR and SEM. The equilibrium swelling ratios of the cryogels were 7.18 g H₂O/g for PHEMA and 6.99 g H₂O/g for PHEMATrp. Lysozyme adsorption experiments were investigated under different conditions in continuous system (i.e., medium pH, flow-rate, protein concentration, temperature, salt type). Lysozyme adsorption capacity of PHEMA and PHEMATrp cryogels from aqueous solutions was estimated as 2.9 and 46.8 mg/g (0.49 and 7.85 mg/mL), respectively. Lysozyme molecules were desorbed with 0.5 M ethylene glycol solution with 91% recovery. It was observed that PHEMATrp cryogel can be used without significant decrease in lysozyme adsorption capacity after five adsorption–desorption cycles. PHEMATrp cryogel was used for the purification of lysozyme from chicken egg white. Purity of lysozyme was estimated by SDS-PAGE. Possible denaturation of purified lysozyme was checked with fluorimetric measurements. Specific activity of the purified lysozyme was found as 43,140 U/mg using Micrococcus lysodeikticus as substrate.     

Synthesis,crystal structure and magnetic properties of the spin crossover system [Fe(pq)3]2+

Three new compounds formulated (ClO₄)₂[Fe(pq)₃] (1), (BF₄)₂[Fe(pq)₃] · EtOH (2) and {(ClO₄)[MnCr(C₂O₄)₃][Fe(pq)₂(H₂O)₂]} (3), where pq is 2,2′-pyridylquinoline, have been synthesised and characterised. Despite the different crystal packing exhibited by 1 and 2, the cationic species [Fe(pq)₃]²⁺ are structurally quite similar. At 293 K, the Fe–N bond lengths are characteristic of the iron(II) in the high-spin state. In contrast to 1, 2 undergoes a continuous spin transition. Indeed, at 95 K its structure experiences a noticeable change in the Fe–N bonds and angles, i.e. the Fe–N bonds shorten by 0.194 Å on the average. The magnetic behaviour confirms that 1 is fully high-spin in the 4–300 K temperature range while 2 shows a spin transition centred at T_1/2 = 150 K. The corresponding enthalpy, entropy and interaction parameter are ΔH = 7.49 kJ mol^?1, ΔS = 50 J K^?1 mol^?1and Γ = 1.35 kJ mol^?1. Compound 3 has been obtained as a microcrystalline powder. The magnetic properties of 3 point at the occurrence of ferromagnetic coupling below 100 K and the onset of a ferromagnetic ordering below 10 K (Weiss constant equal to 6.8 K). The Mössbauer spectra of 3 show the occurrence of a magnetic order at T ? 4.2 K.     

Relaxation dynamics in three polypyridyl iron(II)-based complexes probed by nanosecond and sub-picosecond transient absorption spectroscopy

The results of a sub-picosecond transient absorption spectroscopy study on a mononuclear and two dinuclear low-spin iron(II) complexes is reported. The dinuclear derivatives are homonuclear (i.e. Fe–Fe) and heterodinuclear (Fe–Zn) in nature. The ligands we used were 2-pyridylmethyl-ketazine and 2-pyridylmethyl-hydrazone. Irradiation was made on the metal-to-ligand CT band occurring around 500 nm. The observed pattern of the relaxation decays is consistent with the population of the metastable ⁵T₂ ligand field state within the first 100 fs after the photon absorption from the three different chromophores. The suggested implication of triplet intermediate states was not detected. The ground state recovery was observed to occur with a time constant of 350 ps for the mononuclear complex and 1600–1800 ps for the two dinuclear complexes.     

Critical assessment of iron binary systems with light rare earths La,Ce, Pr,and Nd

Literature data regarding phase equilibria and crystal structure data in the R–Fe systems with R = La, Ce, Pr, Nd have been assessed and the corresponding phase diagrams are presented and discussed. Selected investigations on other constitutive properties (such as magnetic, electronic, thermodynamic) of the R–Fe alloys are also briefly reported.Owing to the numerous investigations some uncertainties remain in the R–Fe phase diagrams and further investigations would be useful.     

Small field characterization of a Nanochamber prototype under flattening filter free photon beams

IntroductionNanochambers present some advantages in terms of energy independence and absolute dose measurement for small field dosimetry in the SBRT scenario. Characterization of a micro-chamber prototype was carried out both under flattened and flattening-filter-free (FFF) beams with particular focus on stem effect.MethodsThe study included characterization of leakage and stem effects, dose rate and dose per pulse dependence, measurement of profiles, and percentage depth doses (PDDs). Ion collection efficiency and polarity effects were measured and evaluated against field size and dose per pulse. The 6_MV, 6_MV_FFF and 10_MV FFF beams of a Varian EDGE were used. Output factors were measured for field sizes ranging from 0.8 × 0.8 cm² to 20 × 20 cm² and were compared with other detectors.ResultsThe 2 mm diameter of this chamber guarantees a high spatial resolution with low penumbra values. In orthogonal configuration a strong stem (and cable) effect was observed for small fields. Dose rate and dose per pulse dependence were <0.3% and 0.6% respectively for the whole range of considered values. The Nanochamber exhibits a field size (FS) dependence of the polarity correction >2%. The OF values were compared with other small field detectors showing a good agreement for field sizes >2 × 2 cm². The large field over-response was corrected applying k_pol(FS).ConclusionsNanochamber is an interesting option for small field measurements. The spherical shape of the active volume is an advantage in terms of reduced angular dependence. An interesting feature of the Nanochamber is its beam quality independence and, as a future development, the possibility to use it for small field absolute dosimetry.     

A conserved lysine residue controls iron–sulfur cluster redox chemistry in Escherichia coli fumarate reductase

The Escherichia coli respiratory complex II paralogs succinate dehydrogenase (SdhCDAB) and fumarate reductase (FrdABCD) catalyze interconversion of succinate and fumarate coupled to quinone reduction or oxidation, respectively. Based on structural comparison of the two enzymes, equivalent residues at the interface between the highly homologous soluble domains and the divergent membrane anchor domains were targeted for study. This included the residue pair SdhB-R205 and FrdB-S203, as well as the conserved SdhB-K230 and FrdB-K228 pair. The close proximity of these residues to the [3Fe–4S] cluster and the quinone binding pocket provided an excellent opportunity to investigate factors controlling the reduction potential of the [3Fe–4S] cluster, the directionality of electron transfer and catalysis, and the architecture and chemistry of the quinone binding sites. Our results indicate that both SdhB-R205 and SdhB-K230 play important roles in fine tuning the reduction potential of both the [3Fe–4S] cluster and the heme. In FrdABCD, mutation of FrdB-S203 did not alter the reduction potential of the [3Fe–4S] cluster, but removal of the basic residue at FrdB-K228 caused a significant downward shift (> 100 mV) in potential. The latter residue is also indispensable for quinone binding and enzyme activity. The differences observed for the FrdB-K228 and Sdh-K230 variants can be attributed to the different locations of the quinone binding site in the two paralogs. Although this residue is absolutely conserved, they have diverged to achieve different functions in Frd and Sdh.     

Evaluation of the technical performance of three different commercial digital breast tomosynthesis systems in the clinical environment

The aim of this work was to research and evaluate the performance of three different digital breast tomosynthesis (DBT) systems in the clinical environment (Siemens Mammomat Inspiration, Hologic Selenia Dimensions, and Fujifilm Amulet Innovality). The characterization included the study of the detector, the automatic exposure control, and the resolution of DBT projections and reconstructed planes.The modulation transfer function (MTF) of the DBT projections was measured with a 1 mm thick steel edge, showing a strong anisotropy (30–40% lower MTF_0.5 frequencies in the tube travel direction). The in-plane MTF_0.5, measured with a 25 μm tungsten wire, ranges from 1.3 to 1.8 lp/mm in the tube-travel direction and between 2.4 and 3.7 lp/mm in the chest wall–nipple. In the latter direction, the MTF peak shift is more emphasized for large angular range systems (2.0 versus 1.0 lp/mm). In-depth resolution of the planes, via the full width at half maximum (FWHM) from the point spread function of a 25 μm tungsten wire, is not only influenced by angular range and yields 1.3–4.6 mm among systems. The artifact spread function from 1 mm diameter tungsten beads depends mainly on angular range, yielding two tendencies whether large (FWHM is 4.5 mm) or small (FWHM is 10 mm) angular range is used. DBT delivers per scan a mean glandular dose between 1.4 and 2.7 mGy for a 45 mm thick polymethyl methacrylate (PMMA) block.In conclusion, we have identified and analysed specific metrics that can be used for quality assurance of DBT systems.     

The first crenarchaeon capable of growth by anaerobic carbon monoxide oxidation coupled with H2 production

The ability to grow by anaerobic CO oxidation with production of H₂ from water is known for some thermophilic bacteria, most of which belong to Firmicutes, as well as for a few hyperthermophilic Euryarchaeota isolated from deep-sea hydrothermal habitats. A hyperthermophilic, neutrophilic, anaerobic filamentous archaeon strain 1505 = VKM B-3180 = KCTC 15798 was isolated from a terrestrial hot spring in Kamchatka (Russia) in the presence of 30% CO in the gas phase. Strain 1505 could grow lithotrophically using carbon monoxide as the energy source with the production of hydrogen according to the equation CO + H₂O → CO₂ + H₂; mixotrophically on CO plus glucose; and organotrophically on peptone, yeast extract, glucose, sucrose, or Avicel. The genome of strain 1505 was sequenced and assembled into a single chromosome. Based on 16S rRNA gene sequence analysis and in silico genome-genome hybridization, this organism was shown to be closely related to the Thermofilum adornatum species. In the genome of Thermofilum sp. strain 1505, a gene cluster (TCARB_0867-TCARB_0879) was found that included genes of anaerobic (Ni,Fe-containing) carbon monoxide dehydrogenase and genes of energy-converting hydrogenase ([Ni,Fe]-CODH–ECH gene cluster). Compared to the [Ni,Fe]-CODH–ECH gene clusters occurring in the sequenced genomes of other H₂-producing carboxydotrophs, the [Ni,Fe]-CODH–ECH gene cluster of Thermofilum sp. strain 1505 presented a novel type of gene organization. The results of the study provided the first evidence of anaerobic CO oxidation coupled with H₂ production performed by a crenarchaeon, as well as the first documented case of lithotrophic growth of a Thermofilaceae representative.     

Reversible lysozyme immobilization onto N,N′-bis-(3-(4-morpholino)-propyl)-3,4,9,10-perylenetetracarboxylic acid dimide (MPPDI) attached polymeric nanospheres

Novel hydrophobic nanospheres with an average size of 200 nm utilizing N,N′-bis-(3-(4-morpholino)-propyl)-3,4,9,10-perylenetetracarboxylic acid dimide (MPPDI) as a monomer were prepared by surfactant free emulsion polymerization of 2-hydroxyethyl methacrylate (HEMA) and MPPDI conducted in an aqueous dispersion medium. The nanospheres were used for the adsorption of lysozyme. The system parameters, such as effect of the adsorption conditions (i.e. enzyme concentration, medium pH, and temperature) and the reusability of the support were studied. Specific surface area of the nonporous nanospheres was found 664 m²/g. Poly(HEMA–MPPDI) nanospheres were characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis and scanning electron microscopy (SEM). Then, poly(HEMA–MPPDI) nanospheres were used in the adsorption of lysozyme in batch system. Using an optimized adsorption protocol, 400 mg lysozyme/g nanosphere loading capacity was obtained. The adsorption phenomena appeared to follow a typical Langmuir isotherm. Lysozyme could be repeatedly adsorbed and desorbed with poly(HEMA–MPPDI) nanospheres without noticeable loss in the adsorption capacity.     

Nanostructured materials for magnetic biosensing

BackgroundMagnetic nanoparticles (MNPs) are at the leading edge of the field of biomedical applications and magnetic biosensing.MethodsMNPs were fabricated by electrophysical methods of the laser target evaporation (LTE) and spark discharge with electrodynamic acceleration of plasma jumpers (SD). Synthesis of polyacrylamide hydrogel was done in the presence of Fe₂O₃ MNPs in different concentrations obtained by LTE. [FeNi/Ti]₃/Cu/[Ti/FeNi]₃/Ti multilayers for giant magnetoimpedance (GMI) based sensitive elements were prepared by rf-sputtering for testing a biosensor prototype.ResultsIron oxide MNPs, ferrofluids, ferrofluids contacting with biological systems, synthetic ferrogels mimicking natural tissues – are the steps of the discussed in this work development of bionanomaterials. Thorough the structural and magnetic studies of a multilayered sensitive element, MNPs and ferrogels insure the complete characterization of biosensor prototype. The GMI responses were carefully evaluated in initial state and in the presence of ferrogel with known concentration of MNPs. SD MNPs had the smallest 5–8 nm size. This nanomaterial was characterized by large internal strains of the order of 25 × 10^− 3, which can play an important role for the interaction with different biosystems.ConclusionsIron oxide MNPs were fabricated by LTE and SD methods. SD MNPs had the smallest 5–8 nm size and large internal strains of the order of 25 × 10^− 3. Designed GMI biosensor prototype allowed precise evaluation of the stray field of the MNPs present in the ferrogel by evaluating the systematic changes of the GMI in a 20–400 MHz frequency range.General significanceThis work summarizes recent developments in the field of nanomaterials potentially applicable in magnetic biosensing.     

Batch and continuous fermentative production of hydrogen with anaerobic sludge entrapped in a composite polymeric matrix

Cell immobilization techniques were adopted to biohydrogen production using immobilized anaerobic sludge as the seed culture. Sucrose-based synthetic wastewater was converted to H₂ using batch and continuous cultures. A novel composite polymeric material comprising polymethyl methacrylate (PMMA), collagen, and activated carbon was used to entrap biomass for H₂ production. Using the PMMA immobilized cells, the favorable conditions for batch H₂ fermentation were 35 °C, pH 6.0, and an 20 g COD l⁻¹ of sucrose, giving a H₂ production rate of 238 ml h⁻¹ l⁻¹ and a H₂ yield of 2.25 mol H₂ mol sucrose⁻¹. Under these optimal conditions, continuous H₂ fermentation was conducted at a hydraulic retention time (HRT) of 4–8 h, giving the best H₂-producing rate of 1.8 l h⁻¹ l⁻¹ (over seven-fold of the best batch result) at a HRT of 6 h and a H₂ yield of 2.0 mol H₂ mol sucrose⁻¹. The sucrose conversion was essentially over 90% in all runs. The biogas consisted of only H₂ and CO₂. The major soluble metabolites were butyric acid, acetic acid, and 2,3-butandiol, while a small amount of ethanol also detected. The PMMA-immobilized-cell system developed in this work seems to be a promising H₂-producing process due to the high stability in continuous operations and the capability of achieving a competitively high H₂ production rate under a relatively low organic loading rate.     

Lorentz force electrical impedance tomography

This article describes a method called Lorentz Force Electrical Impedance Tomography. The electrical conductivity of biological tissues can be measured through their sonication in a magnetic field: the vibration of the tissues inside the field induces an electrical current by Lorentz force. This current, detected by electrodes placed around the sample, is proportional to the ultrasonic pressure, to the strength of the magnetic field and to the electrical conductivity gradient along the acoustic axis. By focusing at different places inside the sample, a map of the electrical conductivity gradient can be established. In this study, experiments were conducted on a gelatin phantom and on a beef sample, successively placed in a 300 mT magnetic field and sonicated with an ultrasonic transducer focused at 21 cm emitting 500 kHz bursts. Although all interfaces are not visible, in this exploratory study a good correlation is observed between the electrical conductivity image and the ultrasonic image. This method offers an alternative to detecting pathologies invisible to standard ultrasonography.     

Observation of optimal gecko's adhesion on nanorough surfaces

In this letter we report experimental observations on the times of adhesion of living Tokay geckos (Gekko geckos) on polymethylmethacrylate (PMMA) inverted surfaces. Two different geckos (male and female) and three surfaces with different root mean square (RMS) roughness (RMS = 42, 618 and 931 nm) have been considered, for a total of 72 observations. The measured data are proved to be statistically significant, following the Weibull Statistics with coefficients of correlation between 0.781 and 0.955. The unexpected result is the observation of a maximal gecko adhesion on the surface with intermediate roughness of RMS = 618 nm, that we note has waviness comparable to the seta size.