Mesorectal failure after chemoradiotherapy for squamous cell carcinoma of the anus: is sphincter-saving surgery reasonable?

BACKGROUND: Abdominoperineal resection (APR) is today the standard treatment for improving survival in case of mesorectal failure without anal canal recurrence after chemoradiotherapy (CRT) for squamous cell carcinoma of the anus (SCC). The aim of this study was to assess if a sphincter-saving surgery is a safe alternative to classical salvage APR in these patients. METHODS: A retrospective study was conducted on all patients who had total mesorectal excision (TME) with sphincter-saving surgery either with coloanal or low colorectal anastomosis, for mesorectal failure after CRT for SCC between 2012 and 2020 at our institution. The main endpoint of our study was oncological results at the end of follow-up. Postoperative morbidity and mortality were secondary endpoints. RESULTS: There were 10 patients, (8 women, median age 55 years [range 45-61 years]). On TME specimens, R0 resections were noted in five (50%), R1 resection in four (40%) and R2 resection in one (10%). After a median follow-up of 42 months (4-74 months), five patients were alive, and four (40%) were alive at 5-year follow-up. During follow-up, locoregional failure after TME was noted in two patients (20%), distant relapse in three patients (30%) and both locoregional plus distant failure in two patients (20%). Only two patients (20%) had anal recurrence, one in the anal canal, the other in the peri-anastomotic area. Long- term local control was achieved in 2 of the 5 patients (40%) who underwent R0 resection versus only 1/4 patients (25%) with R1 resection. CONCLUSIONS: Our preliminary study suggested that sphincter-saving surgery could be proposed in selected patients with SCC presenting mesorectal failure after CRT, providing a feasible R0 resection.

Stroke Work Damping Ratio is Increased in Trained Athletes.

INTRODUCTION: Athletes training is often associated with morphological changes in the heart. In this sense, the ventricular pressure-volume (PV) relation provides a complete characterization of cardiac pump performance. Regarding the arterial system (AS), arterial wall viscosity is a source of energy dissipation, that takes place during mechanical transduction. Left ventricular stroke work (SW) constitutes the useful fraction of ventricular energy that is delivered to the AS. OBJECTIVE: Left ventricular PV-loops were evaluated in terms of AS viscous property, by means of the interaction of two SW components (Stroke Work Damping Ratio, SWDR), both in untrained and trained subjects. MATERIAL AND METHODS: Fourteen healthy individuals (seven trained) were noninvasively evaluated in terms of echocardiographic and aortic pressure measurements. RESULTS: SWDR was observed to be increased in trained subjects. CONCLUSION: SWDR was evaluated in trained individuals, being increased in comparison with the non-trained group. This effect is a consequence of a significant increase of SWD, which could be related with the viscous mechanical property of AS.

Arterial-Ventricular Coupling Impairment is Evidenced in Both Normal and Ischemic Subjects by Applying Cluster Analysis.

INTRODUCTION: Left ventricular (LV) interaction with the arterial system (arterial-ventricular coupling, AVC) is a central determinant of cardiovascular performance and cardiac energetics. Stress Echocardiography (SE) constitutes a valuable clinical tool in both diagnosis and risk stratification of patients with suspected and established coronary artery disease. Cluster Analysis (CA), an unsupervised Machine Learning technique, defines an exploratory statistical method which can be used to uncover natural groups within data. OBJECTIVE: To evaluate the capacity of CA to identify uncoupled groups with ischemic condition based on SE baseline information. MATERIAL AND METHODS: CA was applied to SE data acquired at baseline and peak exercise (PE) conditions. Obtained clusters were evaluated in terms of coupling conditions and LV wall motility alterations. RESULTS: Inter cluster significant AVC differences were obtained in terms of baseline data and changes in wall motility, confirmed by CA applied to PE data. CONCLUSION: AVC impairment was evidenced in both normal and ischemic subjects by applying CA.

Key Role of Deep Orbitals in the dx2-y2-d3z2-r2 Gap in Tetragonal Complexes and 10Dq.

Using first-principles calculations, we show that the origin of the intrinsic a1g(∼3z2 - r2)-b1g(∼x2 - y2) splitting, Δint, in tetragonal transition-metal complexes and the variations of the cubic field splitting, 10Dq, with the metal-ligand distance, R, are much more subtle than commonly thought. As a main novelty, the key role played by covalent bonding with deep valence ligand levels and thus the inadequacy of too simple models often used for the present goal is stressed. Taking as a guide the isolated D4h CuF64- complex, it is proved that Δint essentially arises from bonding with deep 2s(F) orbitals despite them lying ∼23 eV below 2p(F) orbitals. This conclusion, although surprising, is also supported by results on octahedral fluoride complexes where the contribution to 10Dq splitting from bonding with 2s(F) orbitals is behind its strong R dependence, stressing that explanations based on the crystal-field approach are simply meaningless.

Arterial-Ventricular Coupling Evaluation in Individuals with Stress-Evidenced Diastolic Dysfunction: A Pilot Study.

INTRODUCTION: Arterial-ventricular coupling (AVC) has been recognized as a key determinant of global cardiovascular performance. Diastolic dysfunction (DD) occurs when inadequate filling of the ventricles is related to an abnormal elevation of intracardiac filling pressures. In some cases, DD is evidenced during cardiac stress, provoked by exercise. OBJECTIVE: To evaluate AVC in individuals with stress evidenced DD, in relation to controls. MATERIALS AND METHODS: Stress echocardiography was applied to assess cardiac function during exercise. Arterial-ventricular coupling was evaluated, based on the assessment of left ventricular and arterial elastances. RESULTS: AVC showed a significant difference at peak exercise compared to controls, basically due to a loss of cardiac contractility. CONCLUSION: The manifestation of AVC coupling imbalance could act as a complementary parameter to support the diagnosis of DD.

Local structure and excitations in systems with CuF64- units: lack of Jahn-Teller effect in the low symmetry compound Na2CuF4.

This work attempts to unveil the similarities and differences between Jahn-Teller (JT) and non-JT systems involving CuF64- units. For achieving this goal, we firstly explore Na2CuF4 and NaF:Cu2+ systems through first principles calculations and pay particular attention to the links between JT and non-JT systems looking at the electronic density of the hole. The results on Na2CuF4 in the monoclinic P21/c space group and also in the parent Pbam structure reveal that the local geometry can be understood as an initial tetragonally compressed CuF64- unit, followed by an additional orthorhombic instability that excludes the JT effect as the origin. Although the present results on NaF:Cu2+ underpin an elongated equilibrium geometry such as that measured for Cu2+ ions in the cubic perovskite KZnF3, the force constant for NaF:Cu2+ is half that for KZnF3:Cu2+. This crucial fact is direct proof of the elastic decoupling of CuF64- from the NaF lattice leading to a JT energy, EJT, which is twice that found for KZnF3:Cu2+. However, both systems have practically the same linear electron-vibration coupling constant, V1e, a relevant fact whose origin is discussed. The final aim of this work concerns the influence of tetragonal and orthorhombic distortions as well as the internal electric field on the A1g-B1g energy gap, Δ, of a variety of systems with CuF64- complexes. Interestingly, it is shown that compounds with orthorhombic instability and an internal electric field can have a Δ value comparable to the JT system NaF:Cu2+. Accordingly, explanations for optical spectra of transition metal compounds based on simple parameterized models can be meaningless. The present study shows that properties displayed by d9 compounds in low symmetry lattices can hardly stem from a static JT effect.

Explaining the optical spectrum of CrF2 and CuF2 model materials: role of the tetragonal to monoclinic instability.

The properties of MF2 (M = Cr, Cu) model compounds are usually interpreted assuming a Jahn-Teller effect leading to elongated MF64- units. By means of the analysis of experimental data and first-principles calculations on both the monoclinic P21/c structure and the parent rutile structure (tetragonal P42/mnm space group), we prove that such an assumption is not correct. It is shown that in MF2 compounds, the MF64- complexes are actually compressed in the parent phase but along a different direction, a situation that is however hidden by an additional orthorhombic instability due to a negative force constant of b2g and b3g modes of the cell. This distortion plays a key role in understanding the high experimental value of the lowest d-d transition energy, E1 = 1.23 and 0.93 eV for CrF2 and CuF2, respectively, when compared to the value E1 = 0.40 eV derived for the Jahn-Teller system of KZnF3:Cu2+. Aside from reproducing reasonably the experimental values of spin allowed d-d transitions of both compounds, our first-principles calculations show the existence of an accidental degeneracy involving the yz and xy levels in the final P21/c structure. Moreover, the internal electric field of CrF2 and CuF2 is found to be much less anisotropic than in layered compounds like K2CuF4 and thus it has little influence on the d-d transition energy. The influence of the (3z2 - r2) - (x2 - y2) hybridization, caused by the orthorhombic distortion, on the electronic density and the magnetic coupling between layers is also briefly discussed. The present results stress that the interpretation of experimental data using simple parameterized models can lead to wrong conclusions.

Hemangiopericitoma intracraneano: Reporte de un caso y revisión del tema / Intracranial Haemangiopericytoma: Case report and literature review

INTRODUCCIÓN: el Hemangiopericitoma (HPC) es un tumor hipervascular infrecuente que constituye menos del 1% de todos los tumores del Sistema Nervioso Central (SNC) y aproximadamente el 3% de los tumores vinculados a las meninges. Son tumores agresivos que requieren un tratamiento enérgico mediante cirugía y radioterapia, y a pesar del mismo, generalmente son tumores recidivantes, pudiendo generar metástasis a distancia. OBJETIVOS: comunicar el primer caso en que se hace diagnóstico con un panel inmunohistoquímico completo de HPC en Uruguay, y a partir del mismo, se realiza una revisión bibliográfica. MATERIALES Y MÉTODO: en primer lugar se presenta un caso clínico de un paciente que fue asistido en el Hospital de Clínicas. Mediante estudios de imagen se sospecha probable HPC, es intervenido quirúrgicamente de coordinación y el diagnóstico definitivo se realiza mediante estudio de anatomía patológica que incluye técnica inmunohistoquímica. A partir de este caso clínico ilustrativo se realizó una puesta al día sobre esta patología. DISCUSIÓN: a nivel intracraneano, los HPC tienen una distribución similar a los meningiomas, con una base de implantación dural. Tal es su similitud con los meningiomas, que fueron considerados como una variante meningoblástica o angiomatosas de los mismos. Desde 1993 se los clasifica como un grupo aparte, presentando 2 variantes: clásica, de bajo grado (grado II) y anaplásico (grado III). El estudio histopatológico (morfológico e inmunohistoquimico) es fundamental ya que los diferencia definitivamente a los meningiomas de los HCP. En cuanto a los marcadores, y siguiendo la bibliografía referente, nuestro caso reportado fue negativo para CD 34 pero positivo para factor VIIIa. CONCLUSIONES: los HPC del SNC son tumores poco frecuentes, con un comportamiento agresivo, tendencia a recurrir y dar metástasis a distancia. Por lo que es fundamental tener siempre presente este tipo de lesiones en patología tumoral de meninges. Un diagnóstico rápido con estudio histológico y confirmación immunohistoquímica permite llegar al diagnostico y a un tratamiento oportuno agresivo, ya que el mismo es lo único que está demostrado que mejora el pronóstico.

INTRODUCTION: the haemangio-pericytoma (HPC) is a rare hypervascular tumor that accounts for less than 1% of all the Central Nervous System (CNS) tumor and approximately 3% of the tumors involving the meninges. They are aggressive tumors that require an energetic therapy including surgery and radiotherapy, despite which the tumors tend to relapse, potentially giving rise to distant metastases. OBJECTIVES: to report the first case where the diagnosis is reached with the comprehensive immuno-histochemistry panel for HPC in Uruguay, and literature review based on that case. MATERIALS AND METHOD: we describe the case of a patient treated at the Hospital de Clínicas. Imaging studies suggested a potential HPC; the patient underwent scheduled surgery and the final diagnosis was reached through the pathology assessment, using immunohistochemistry. A literature review of the condition is presented on the basis of the clinical report. DISCUSSION: at an intracranial level, HPCs have a distribution similar to that of meningiomas, with a dural implantation. They are so much alike meningiomas that they were considered to be a meningoblastic or angiomatous variant of those tumors. Since 1993 they are classified as a separate group with 2 variations: classical, low-grade (grade II) and anaplastic (grade III). The histology test (morphological and immunohistochemistry) is essential, since it reveals the differences between HCPs and meningiomas. As to markers, in accordance with the bibliography, our case was reported as negative for CD 34 but was positive for factor VIIIa. CONCLUSIONS: SNC HPCs are uncommon tumors that behave aggressively; they tend to relapse and cause distant metastases. Hence, it is always crucial to bear this diagnosis in mind when facing a meningeal tumor. A quick diagnosis including histology and immuno-histochemical confirmation allows for a timely aggressive therapy- the only thing that improves prognosis.

Quantifying local and cooperative components in the ferroelectric distortion of BaTiO(3): learning from the off-center motion in the MnCl(6)(5-) complex formed in KCl:Mn(+).

The delicate balance between cooperative and local contributions in the ferroelectric distortions of BaTiO3 is explored by means of ab initio calculations. As a salient feature, it is found that a single Ti(4+) ion in BaTiO3 is not allowed to move off-center at ambient pressure, while this is no longer true if the lattice is expanded by only ∼5%, stressing the high sensitivity of the local contribution to chemical and hydrostatic pressures. In order to further understand the effect of local contributions on the phase transition mechanism of ferroelectrics, we have investigated the surprising C3v → C4v → Oh local transformations occurring in the 10-50 K temperature range for the MnCl6(5-) complex formed in KCl:Mn(+) that mimic the behavior of BaTiO3. From Boltzmann analysis of the vibronic levels derived from ab initio calculations and considering decoherence introduced by random strains, the present calculations reproduce the experimental phase sequence and transition temperatures. Furthermore, our calculations show that the off-center instability in KCl:Mn(+) would be suppressed by reducing by only 1% the lattice parameter, a situation that then becomes comparable to that found for BaTiO3 at ambient pressure. The present results thus stress the deep link between the structural phase transitions of ferroelectric materials and local phase transitions displayed by transition-metal impurities in insulators.

Sharp lines due to Cr³âº and Mn²âº impurities in insulators: going beyond the usual Tanabe-Sugano approach.

This work is aimed at understanding the different behavior of optical sharp lines (corresponding to 10Dq-independent transitions) of Mn(2+) and Cr(3+) in normal and inverted perovskites that cannot be explained within the usual Tanabe-Sugano approach. In particular, we want to clarify why on passing from KMgF3:M to LiBaF3:M (M = Mn(2+), Cr(3+)) the energy, E((6)A1 → (4)A1), for Mn(2+) decreases by Δ = 1100 cm(-1), while Δ < 100 cm(-1) for the energy E((2)E →( 4)A2) corresponding to Cr(3+). The origin of this surprising difference in these model systems is clarified by writing the transition energies of MF6 complexes through the ten Coulomb and exchange integrals consistent with the cubic symmetry and not considered in the usual Tanabe-Sugano approach. It is shown that E((6)A1 → (4)A1) depends on exchange integrals K(3z(2) - r(2), xy) and K(x(2) - y(2), xy), while E((2)E → (4)A2) depends on K(xz, yz) where the two involved electrons display a π character. These exchange integrals have been calculated just considering a MF6 unit subject to the internal electric field due to the rest of the lattice ions. In addition to a reasonably reproduction of the main trends observed experimentally for the model systems, the present calculations prove that the exchange integrals are not related in a simple way to the covalency of involved orbitals. Particular attention is also paid to explain why the transitions, which are 10Dq-independent are less sensitive to the host lattice change than those which do depend on 10Dq. The present work shows that K(xz, yz) for Cr(3+) is particularly insensitive to the host lattice change and thus sheds light on the origin of the near independence of E((2)E → (4)A2) along the series of oxides doped with such an impurity .

Transition metal complexes coupled to vacancies in oxides: origin of different properties of Cr3+ in MgO bounded to a <100> or <110> Mg2+ vacancy.

Despite the importance of vacancies over the properties of insulating oxides its influence on neighboring transition metal ions is far from being understood. This work is devoted to find the origin of various up to now unexplained properties of chromium bounded either to a <100> or a <110> Mg(2+) vacancy in MgO. In these model systems particular attention is paid to understand, by means of ab initio calculations, why the cubic field splitting parameter, 10Dq, is surprisingly 1600 cm(-1) higher for a <100> than for a <110> vacancy, a fact behind the suppression of the sharp (2)E → (4)A2 luminescence in the latter case. Our calculations, which reproduce the main experimental facts, prove that the average Cr(3+)-O(2-) distance is the same within 0.8% for both systems, and thus, the low 10Dq value for a <110> vacancy is shown to be due mainly to the electrostatic potential from the missing Mg(2+) ion, which increases the energy of antibonding t(2g) (∼xy, xz, yz) levels. By contrast, for a <100> Mg(2+) vacancy that potential provides a supplementary increase of the e(g) (∼x(2) - y(2), 3z(2 )- r(2)) level energy and thus of 10Dq. The existence of the (2)E → (4)A2 luminescence for Cr(3+)-doped MgO under perfect cubic symmetry or with a <100> vacancy is shown to be greatly helped by the internal electric field created by the rest of the lattice ions on the CrO6(9-) unit, whose importance is usually ignored. The present results underline the role of ab initio calculations for unveiling the subtle effects induced by a close vacancy on the properties of transition metal ions in oxides. At the same time they stress the failure of the empirical superposition model for deriving the equilibrium geometry of C4v and C2v centers in MgO:Cr(3+).

Origin of small barriers in Jahn-Teller systems: quantifying the role of 3d-4s hybridization in the model system NaCl:Ni+.

Despite its relevance, the microscopic origin of the energy barrier, B, between the compressed and elongated geometries of Jahn-Teller (JT) systems is not well understood yet because of a lack of quantitative data about its various contributions. Seeking to clear up this matter, we have carried out both periodic and cluster ab initio calculations on the model system NaCl:Ni(+). This system is particularly puzzling because, according to experimental data, its barrier is much smaller than that for other d(9) and d(7) ions in similar lattices. All calculations performed on the model system lead, in fact, to values |B| ≤ 160 cm(-1), which are certainly smaller than B = 500 cm(-1) derived for NaCl:M(2+) (M = Ag, Rh) or B = 1024 cm(-1) obtained for KCl:Ag(2+). As a salient feature, analysis of calculations carried out as a function of the Qθ (∼3z(2) - r(2)) coordinate unveils the microscopic origin of the barrier. It is quantitatively proven that the elongated geometry observed for NaCl:Ni(+) is due to the 3d-4s vibronic admixture, which is slightly larger than the anharmonicity in the eg JT mode that favors a compressed geometry. The existence of these two competing mechanisms explains the low value of B for the model system, contrary to cases where the complex formed by d(9) or d(7) ions is elastically decoupled from the host lattice. Although the magnitude of B for NaCl:Ni(+) is particularly small, the tunneling splitting, 3Γ, is estimated to be below 9 cm(-1), thus explaining why the coherence is easily destroyed by random strains and thus a static JT effect is observed experimentally. As a main conclusion, the barrier in JT systems cannot be understood neglecting the tiny changes of the electronic density involved in small distortions. The present calculations reasonably explain the experimental g tensor of NaCl:Ni(+), pointing out that the d-d transitions in NiCl6(5-) are much smaller than those for CuCl6(4-) and the optical electronegativity of Ni(+) is only around 1.

Cu2+ in layered compounds: origin of the compressed geometry in the model system K2ZnF4:Cu2+.

Many relevant properties (including superconductivity and colossal magnetoresistance) of layered materials containing Cu(2+), Ag(2+), or Mn(3+) ions are commonly related to the Jahn-Teller instability. Along this line, the properties of the CuF6(4-) complex in the K2ZnF4 layered perovskite have recently been analyzed using a parametrized Jahn-Teller model with an imposed strain [Reinen, D. Inorg. Chem.2012, 51, 4458]. Here, we present results of ab initio periodic supercell and cluster calculations on K2ZnF4:Cu(2+), showing unequivocally that the actual origin of the unusual compressed geometry of the CuF6(4-) complex along the crystal c axis in that tetragonal lattice is due to the presence of an electric field due to the crystal surrounding the impurity. Our calculations closely reproduce the experimental optical spectrum. The calculated values of the equilibrium equatorial and axial Cu(2+)-F(-) distances are, respectively, R(ax) = 193 pm and R(eq) = 204 pm, and so the calculated distortion R(ax) - R(eq) = 11 pm is three times smaller than the estimated through the parametrized Jahn-Teller model. As a salient feature, we find that if the CuF6(4-) complex would assume a perfect octahedral geometry (R(ax) = R(eq) = 203 pm) the antibonding a(1g)*(∼3z(2) - r(2)) orbital is placed above b(1g)*(∼x(2) - y(2)) with a transition energy E((2)A(1g) → (2)B(1g)) = 0.34 eV. This surprising fact stresses that about half the experimental value E((2)A(1g) → (2)B(1g)) = 0.70 eV is not due to the small shortening of the axial Cu(2+)-F(-) distance, but it comes from the electric field, E(R)(r), created by the rest of the lattice ions on the CuF6(4-) complex. This internal field, displaying tetragonal symmetry, is thus responsible for the compressed geometry in K2ZnF4:Cu(2+) and the lack of symmetry breaking behind the ligand relaxation. Moreover, we show that the electronic energy gain in this process comes from bonding orbitals and not from antibonding ones. The present results underline the key role played by ab initio calculations for unveiling all the complexity behind the properties of the model system K2ZnF4:Cu(2+), opening at the same time a window for improving our knowledge on d(9), d(7), or d(4) ions in other layered compounds.

Colour due to Cr3+ ions in oxides: a study of the model system MgO:Cr3+.

Seeking to understand why the cubic centre in MgO:Cr(3+) has the same 10Dq value as emerald, ab initio cluster and periodic supercell calculations have been performed. It is found that the equilibrium Cr(3+)-O(2-) distance, R, in MgO:Cr(3+) is equal to 2.03 Å and thus 0.06 Å higher than that measured for the emerald. Calculations carried out on the isolated CrO(6)(9-) complex at R = 2.03 Å give 10Dq = 14,510 cm(-1), which is 10% smaller than the experimental figure for MgO:Cr(3+). Nevertheless, when the internal electric field, ER(r), due to the rest of the lattice ions is also taken into account, the calculated 10Dq = 16,210 cm(-1) coincides with the experimental value. Accordingly, the colour shift for different oxides doped with Cr(3+) can be well understood on the basis of this extrinsic contribution to 10Dq usually ignored in a ligand field description. The calculated electrostatic potential, VR(r), related to ER(r), is found to be attractive when the electronic density is lying along <110> directions and |r| > 1 Å driven by the first shell of twelve Mg(2+) ions. The action of VR(r) upon the CrO(6)(9-) complex slightly decreases the energy of t2g(xy,xz,yz) orbitals with respect to that for eg(3z(2) - r(2),x(2) - y(2)) orbitals, thus enhancing the 10Dq value by 0.2 eV. However, the addition of VR(r) induces very small changes in the electronic density, a relevant fact that is related to the (2)E(t(2g)(3)) −> (4)A(2)(t(2g)(3)) emission energy being nearly independent of the host lattice along the series of Cr(3+)-doped oxides.

Complete nucleotide sequence of a severe isolate of cucumber vein yellowing virus from Jordan.

The complete genome of a severe isolate of Cucumber vein yellowing virus (CVYV) from Jordan was sequenced. Comparison with the genome of a Spanish CVYV isolate inducing very mild symptoms in cucumber cultivars revealed a nucleotide identity of 94% for the complete genome and an amino acid identity of 96% for the coding region. Comparison of synonymous and non-synonymous substitutions suggested a negative selection at amino acid and nucleotide levels with different degrees depending on the different coding regions. Finally, specific amino acid changes in the zinc finger domain of P1b and in the P1-P3 proteolytic site were found which could be involved in the virulence of CVYV.

Cr3+-doped fluorides and oxides: role of internal fields and limitations of the Tanabe-Sugano approach.

This work is aimed at clarifying the changes on optical spectra of Cr(3+) impurities due to either a host lattice variation or a hydrostatic pressure, which can hardly be understood by means of the usual Tanabe-Sugano (TS) approach assuming that the Racah parameter, B, grows when covalency decreases. For achieving this goal, the optical properties of Cr(3+)-doped LiBaF(3) and KMgF(3) model systems have been explored by means of high level ab initio calculations on CrF(6)(3-) units subject to the electric field, E(R)(r), created by the rest of the lattice ions. These calculations, which reproduce available experimental data, indicate that the energy, E((2)E), of the (2)E(t(2g)(3)) → (4)A(2)(t(2g)(3)) emission transition is nearly independent of the host lattice. By contrast, the energy difference corresponding to (4)A(2)(t(2g)(3)) → (4)T(1)(t(2g)(2)e(g)(1)) and (4)A(2)(t(2g)(3)) → (4)T(2)(t(2g)(2)e(g)(1)) excitations, Δ((4)T(1); (4)T(2)), is shown to increase on passing from the normal to the inverted perovskite host lattice despite the increase in covalency, a fact which cannot be accounted for through the usual TS model. Similarly, when the Cr(3+)-F(-) distance, R, is reduced both Δ((4)T(1); (4)T(2)) and the covalency are found to increase. By analyzing the limitations of the usual model, we found surprising results that are shown to arise from the deformation of both 3d(Cr) and ligand orbitals in the antibonding e(g) orbital, which has a σ character and is more extended than the π t(2g) orbital. By contrast, because of the higher stiffness of the t(2g) orbital, the dependence of E((2)E) with R basically follows the corresponding variation of covalency in that level. Bearing in mind the similarities of the optical properties displayed by Cr(3+) impurities in oxides and fluorides, the present results can be useful for understanding experimental data on Cr(3+)-based gemstones where the local symmetry is lower than cubic.

Detection, discrimination and absolute quantitation of Tomato spotted wilt virus isolates using real time RT-PCR with TaqMan(®)MGB probes.

A quantitative real-time reverse transcription-polymerase chain reaction (RT-qPCR) procedure using a general primer set and three TaqMan(®)MGB probes was developed for general and genotype-specific detection and quantitation of the genomic M segment of Tomato spotted wilt virus (TSWV). Standard curves using RNA transcripts homologous to the three probes allowed reproducible quantitative assays with a wide dynamic range (10(3)-10(10) TSWV M segment RNA copies/ng of total RNA) and high sensitivity. This protocol was assayed with a battery of TSWV isolates, covering the range of the present known genetic variation, in single and/or mix infections in three plant hosts, as well as in the thrips vector Frankliniella occidentalis. This quantitative detection assay will be a valuable tool for molecular biology and epidemiology studies, diagnosis and disease control.

Spectrochemical series and the dependence of Racah and 10 Dq parameters on the metal-ligand distance: microscopic origin.

The origin of the spectrochemical series and the different dependence of crystal-field splitting (10Dq) and Racah parameters on the metal-ligand distance, R, is explored through ab initio calculations on Cr(3+)-doped K2NaScF6, Cs2NaYCl6, Cs2NaYBr6, and Cs2NaYI6 lattices. For this purpose both periodic and cluster calculations have been performed. An analysis of ab initio results proves that 10Dq values mostly come from the small admixture of deep nLs ligand orbitals present in the antibonding eg(∼ x(2)-y(2),3z(2)-r(2)) level and not from the dominant covalency with valence nLp ligand orbitals, which is actually responsible for the reduction of Racah parameters. This study thus reveals the microscopic origin of the stronger dependence upon R of 10Dq when compared to that observed for Racah parameters, thus explaining why electronic transitions which are 10Dq-independent give rise to sharp optical bands. As a salient feature, while the covalency with nLp levels increases significantly on passing from CrF6(3-) to CrI6(3-), the nLs admixture in eg is found to be practically unmodified. This fact helps to understand the progressive decrease of 10Dq through the series of CrF6(3-), CrCl6(3-), CrBr6(3-), and CrI6(3-) complexes embedded in the corresponding host lattices when compared at the corresponding equilibrium distance at zero pressure. The growing importance of the nLs admixture is well-depicted using deformation density diagrams on passing from the ground state (4)A2(t2g(3)) to the (4)T2(t2g(2)eg) excited state depicted at several R values.

Tunneling splitting of Jahn-Teller ions in oxides.

The magnitude of tunneling splitting, 3Gamma, that governs decoherence in quantum systems under symmetric potentials, is frequently unknown. Using first-principles calculations, we have obtained 3Gamma for a number of E[symbol:see text]e Jahn-Teller impurities in solids. Calculated values span 6 orders of magnitude on passing from KCl:Ag{2+} to MgO:Cu{2+}. Values associated with Cu2+- and Ag2+-doped MgO are 2 orders of magnitude larger than those previously assumed and consistent with the existence of a dynamic Jahn-Teller effect. The origin and enhancement with pressure of these high 3Gamma values is discussed in detail.

Cr3+ in layered perovskites: do the electron paramagnetic resonance parameters only depend on the impurity-ligand distances?

The actual value of axial, R(ax), and equatorial, R(eq), impurity-ligand distances for Cr(3+) embedded in tetragonal K(2)MgX(4) (X = F, Cl) lattices has been explored by means of density functional theory (DFT) calculations on clusters involving up to 69 ions using two different functionals. For K(2)MgF(4):Cr(3+) R(eq) and R(ax) are found to be coincident within only 0.5 pm. When the g tensor of K(2)MgF(4):Cr(3+) is derived considering only the CrF(6)(3-) unit in vacuo at the calculated equilibrium geometry the g(⊥)-g(||) quantity fails to reproduce the experimental value by one order of magnitude. In contrast, when the active electrons localized in the CrX(6)(3-) complex (X = F, Cl) are allowed to feel the anisotropic electric field coming from the rest of the lattice ions the splitting in the first excited state, (4)T(2), increases by one order of magnitude. The present results thus show that the g tensor anisotropy and the zero-field splitting constant, D, observed for K(2)MgX(4):Cr(3+) (X = F, Cl) are not mainly due to a local deformation of the CrX(6)(3-) octahedron but to the action of the internal electric field, often ignored when seeking the microscopic origin of electronic properties due to impurities in insulating lattices. Accordingly, serious doubts on the validity of the superposition model are cast by the present work.