Aristotle on identity: close enough!

We present what Aristotle wrote on identity in a leisurely manner, which is much more than is generally known, save among the cognoscenti (Aristotle scholars), and mutatis mutandis about the introduction of the identity-symbol [Formula: see text]. We add two codas, one on the so-called Leibniz' Law, which is different (but resembles) what passes for it in logic and philosophy, and one on the status of identity, as accepted by mathematicians and logicians, in physics. This article is part of the theme issue 'Identity, individuality and indistinguishability in physics and mathematics'.

Gas phase condensation of superparamagnetic iron oxide-silica nanoparticles--control of the intraparticle phase distribution.

Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs consisting of a γ-Fe2O3 and a SiO2 hemisphere to γ-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple γ-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis.

Ion adsorption behaviour of hydroxyapatite with different crystallinities.

This study aimed to correlate crystallinity of hydroxyapatite (HA) with the ion adsorption behaviour of the material. Hydroxyapatite powders of various crystallinities (X(c)) and specific surface area (SSA) were prepared by precipitation following heat treatment. Adsorption experiments were carried out by using (i) multi-component ion solutions containing a broad range of light and heavy ions to study competitive adsorption and (ii) lead and zinc solutions with concentrations up to 250 ppm to determine the adsorption isotherms of the material. While as-prepared HA powders of low crystallinity (X(c)=0%) and a high SSA of 170 m(2)/g showed quantitative removal for divalent Pb, Zn, Be, U, Bi, V, Al, Cu and Ga ions, calcined powders with higher crystallinity (X(c)=65-95%) and lower SSA between 5 and 30 m(2)/g led to a quantitative removal only for a few elements (Pb, Bi, Ga). The time and concentration dependant ion removal capacity for Pb(2+) and Zn(2+) single element solutions showed quantitative removal even after short immersion times of less than 10 min for as-prepared HA powders. XRD analysis of the powders after ion adsorption revealed the presence of pyromorphite (Pb(5)(PO(4))(3)OH) and hopeite (Zn(3)(PO(4))(2)) phases, respectively.

The structure of titanate nanobelts used as seeds for the nucleation of hydroxyapatite at the surface of titanium implants.

The sequence of steps of a chemical treatment having as its goal the induce of nucleation and the growth of hydroxyl carbonated apatite (HCA) at the surface of titanium implants was studied by scanning and transmission electron microscopy in cross-section. In the first step, an acid etching forms a rough titanium hydride layer, which remains unchanged after subsequent treatments. In the second step, soaking in an NaOH solution induces the growth of nanobelt tangles of nanocrystallized, monoclinic sodium titanate. In the third step, soaking in simulated body fluid transforms sodium titanate into calcium titanate by ion-exchange in the monoclinic structure. HCA then grows and embodies the tangled structure. The interfaces between the different layers seem to be strong enough to prevent interfacial decohesion. Finally, the role of the titanate structure in the nucleation process of HCA is discussed.

Development of graded hydroxyapatite/CaCO(3) composite structures for bone ingrowth.

Ceramic composites composed of constituents with different bone cell reactions present an interesting consideration for a new bone replacement material. The first component of the composite used in this study, hydroxyapatite, is known to be replaced by natural tissue significantly slower than the second, calcium carbonate, which has limited structural stability. A graded hydroxyapatite/calcium carbonate composite with bimodal component distribution was developed using a combined slip infiltration and dip-coating technique from a porous polyurethane sponge replica. A graded hydroxyapatite scaffold with porosities from 5 to 90% was produced and then infiltrated with a calcium carbonate slip and sintered. The resultant composite had improved mechanical properties compared with the monolith as measured by crushing and moduli tests.

Sonochemical synthesis of calcium phosphate powders.

beta-tricalcium phosphate (beta-TCP) and biphasic calcium phosphate powders (BCP), consisting of hydroxyapatite (HA) and beta-TCP, were synthesized by thermal decomposition of precursor powders obtained from neutralization method. The precursor powders with a Ca/P molar ratio of 1.5 were prepared by adding an orthophosphoric acid (H(3)PO(4)) solution to an aqueous suspension containing calcium hydroxide (Ca(OH)(2)). Mixing was carried out by vigorous stirring and under sonochemical irradiation at 50 kHz, respectively. Glycerol and D-glucose were added to evaluate their influence on the precipitation of the resulting calcium phosphate powders. After calcination at 1000 degrees C for 3 h BCP nanopowders of various HA/beta-TCP ratio were obtained.

Influence of magnesium doping on the phase transformation temperature of beta-TCP ceramics examined by Rietveld refinement.

The influence of Mg doping in Ca(3)(PO(4))(2) on the transformation temperature of beta-tricalcium phosphate (beta-TCP) to alpha-tricalcium phosphate (alpha-TCP) was examined. A maximum substitution by 14 mol% of Mg(2+) on Ca(2+) sites in the beta-TCP structure was determined for powders calcinated at 1025+/-10 degrees C. X-ray powder diffraction analysis (XRPD) in combination with Rietveld method (TOPAS 2.1) was employed for quantitative phase analysis and structural refinement. The synthesized and characterized Mg-doped samples were sintered in air atmosphere in a vertical tube furnace at suitable temperatures ranging from 1460 to 1680 degrees C and subsequently quenched to room temperature, in order to stabilize alpha-TCP. The beta to alpha transformation temperatures were determined by differential temperature analysis and XRPD analysis.

[Method and clinical significance of cerebrospinal fluid spectrophotometry]. / Methode und klinische Bedeutung der Liquorspektrophotometrie.

The results of the spectrophotometric analysis of 932 cerebrospinal fluid specimens are presented. The specimens were obtained from 95 patients with subarachnoid and intracerebral hemorrhages, 75 patients with traumatic head injuries, 40 patients with infectious diseases of the central nervous system, 302 patients with cerebrovascular accidents and 302 patients suffering from a variety of diseases such as multiple sclerosis, herniated intervertebral discs and vasomotor headache. Normal cerebrospinal fluid is colourless and shows a spectrophotometric absorption characterized by a flat curve with decreasing absorption from 350 to 650 nm. In disease states Oxy-Hemoglobin, Met-Hemoglobin and Bilirubin can be identified in cerebrospinal fluid. These pigments, when present in cerebrospinal fluid, change the spectrophotometric curve due to their specific absorption spectra. According to the quantitative relationship between the pigments and their chronological order of appearance in the cerebrospinal fluid, typical spectrophotometric patterns have been delineated. The spectrophotometric absorption curve of a hemorrhage due to rupture differs from that of a diapedetic hemorrhage. Moreover, tap bleeding results in an absorption curve which can be differentiated early from that of a subarachnoid hemorrhage. Finally, artifacts due to desinfectants can easily be identified. It is concluded that the spectrophotometric analysis of cerebrospinal fluid gives helpful information in subarachnoidal-hemorrhage, subdural and intracerebral hematoma, in contusions of the brain, carcinomatosis of the leptomeninx, spinal tumor and meningoencephalitis of unknown origin.

Cerebrospinal fluid immunoglobulins and multiple sclerosis. Correspondence with magnetic resonance imaging and visually evoked potential changes.

The clinical (disability) and paraclinical (visually evoked potential [VEP]/magnetic resonance imaging [MRI]) data of patients with definite or probable multiple sclerosis (MS) were compared with their cerebrospinal fluid (CSF) immunoglobulins taken within the same period of time. For patients with definite diagnosis by the Schumacher criteria (n = 61) we found significant correlations between CSF immunoglobulin content (absolute gamma-globulin value [aggv]) and quantified MRI factors (r = .47), between aggv and the sum of VEP latencies of both eyes (r = .53), and also between MRI and VEP changes (r = .62). This was not true for the patients with a probable MS diagnosis and for patients with first attacks. No correlations were evident between aggv and disability status or duration of the illness. The results give support to recent neuropathologic and experimental findings in animals indicating close pathogenic connections between CSF immunoglobulins and demyelination in MS.

[The influence of endogenous insulin and glucagon on the free fatty acids in the circulating blood plasma]. / Die invloed van endogene insulien en glukagon op die vry vetsure in die sirkulerende bloedplasma.

The effect of increased endogenous plasma insulin and glucagon concentrations on the free fatty acid (FFA) levels in the circulating blood was investigated in sheep, 2 baboons and 1 vervet monkey. Elevation of the plasma insulin level was obtained by vagal stimulation or intravenous glucose administration and vagal stimulation, whereas increased glucagon levels were induced by sympathetic stimulation, increased plasma insulin levels, with simultaneous increased plasma glucose concentrations (in our experiments with sheep), produced a pronounced lowering of the FFA levels. From this observation a lipogenetic function could be ascribed to insulin. However, in the primate experiments, increased plasma insulin without concomitant glucose administration caused an elevation of FFA levels, and would indicate a lipolytic rather than a lipogenetic action of insulin. Increased glucagon levels, as produced by sympathetic stimulation, did not alter the FFA concentrations significantly. It thus appears that glucagon has no lipolytic effect, as claimed by previous investigators. In our experiment on the vervet monkey, sympathetic stimulation, with increased plasma glucagon, even caused a decrease in FFA levels.