Head Reduction Osteotomy With Additional Containment Surgery Improves Sphericity and Containment and Reduces Pain in Legg-Calvé-Perthes Disease.

BACKGROUND Severe femoral head deformities in the frontal plane such as hips with Legg-Calvé-Perthes disease (LCPD) are not contained by the acetabulum and result in hinged abduction and impingement. These rare deformities cannot be addressed by resection, which would endanger head vascularity. Femoral head reduction osteotomy allows for reshaping of the femoral head with the goal of improving head sphericity, containment, and hip function. QUESTIONS/PURPOSES Among hips with severe asphericity of the femoral head, does femoral head reduction osteotomy result in (1) improved head sphericity and containment; (2) pain relief and improved hip function; and (3) subsequent reoperations or complications? METHODS Over a 10-year period, we performed femoral head reduction osteotomies in 11 patients (11 hips) with severe head asphericities resulting from LCPD (10 hips) or disturbance of epiphyseal perfusion after conservative treatment of developmental dysplasia (one hip). Five of 11 hips had concomitant acetabular containment surgery including two triple osteotomies, two periacetabular osteotomies (PAOs), and one Colonna procedure. Patients were reviewed at a mean of 5 years (range, 1-10 years), and none was lost to followup. Mean patient age at the time of head reduction osteotomy was 13 years (range, 7-23 years). We obtained the sphericity index (defined as the ratio of the minor to the major axis of the ellipse drawn to best fit the femoral head articular surface on conventional anteroposterior pelvic radiographs) to assess head sphericity. Containment was assessed evaluating the proportion of patients with an intact Shenton's line, the extrusion index, and the lateral center-edge (LCE) angle. Merle d'Aubigné-Postel score and range of motion (flexion, internal/external rotation in 90° of flexion) were assessed to measure pain and function. Complications and reoperations were identified by chart review. RESULTS At latest followup, femoral head sphericity (72%; range, 64%-81% preoperatively versus 85%; range, 73%-96% postoperatively; p = 0.004), extrusion index (47%; range, 25%-60% versus 20%; range, 3%-58%; p = 0.006), and LCE angle (1°; range, -10° to 16° versus 26°; range, 4°-40°; p = 0.0064) were improved compared with preoperatively. With the limited number of hips available, the proportion of an intact Shenton's line (64% versus 100%; p = 0.087) and the overall Merle d'Aubigné-Postel score (14.5; range, 12-16 versus 15.7; range, 12-18; p = 0.072) remained unchanged at latest followup. The Merle d'Aubigné-Postel pain subscore improved (3.5; range, 1-5 versus 5.0; range, 3-6; p = 0.026). Range of motion was not observed to have improved with the numbers available (p ranging from 0.513 to 0.778). In addition to hardware removal in two hips, subsequent surgery was performed in five of 11 hips to improve containment after a mean interval of 2.3 years (range, 0.2-7.5 years). Of those, two hips had triple osteotomy, one hip a combined triple and valgus intertrochanteric osteotomy, one hip an intertrochanteric varus osteotomy, and one hip a PAO with a separate valgus intertrochanteric osteotomy. No avascular necrosis of the femoral head occurred. CONCLUSIONS Femoral head reduction osteotomy can improve femoral head sphericity. Improved head containment in these hips with an often dysplastic acetabulum requires additional acetabular containment surgery, ideally performed concomitantly. This can result in reduced pain and avascular necrosis seems to be rare. With the number of patients available, function did not improve. Therefore, future studies should use more precise instruments to evaluate clinical outcome and include longer followup to confirm joint preservation. LEVEL OF EVIDENCE Level IV, therapeutic study.

A Deletion in the VLDLR Gene in Eurasier Dogs with Cerebellar Hypoplasia Resembling a Dandy-Walker-Like Malformation (DWLM).

Dandy-Walker-like malformation (DWLM) is the result of aberrant brain development and mainly characterized by cerebellar hypoplasia. DWLM affected dogs display a non-progressive cerebellar ataxia. Several DWLM cases were recently observed in the Eurasier dog breed, which strongly suggested a monogenic autosomal recessive inheritance in this breed. We performed a genome-wide association study (GWAS) with 9 cases and 11 controls and found the best association of DWLM with markers on chromosome 1. Subsequent homozygosity mapping confirmed that all 9 cases were homozygous for a shared haplotype in this region, which delineated a critical interval of 3.35 Mb. We sequenced the genome of an affected Eurasier and compared it with the Boxer reference genome and 47 control genomes of dogs from other breeds. This analysis revealed 4 private non-synonymous variants in the critical interval of the affected Eurasier. We genotyped these variants in additional dogs and found perfect association for only one of these variants, a single base deletion in the VLDLR gene encoding the very low density lipoprotein receptor. This variant, VLDLR:c.1713delC is predicted to cause a frameshift and premature stop codon (p.W572Gfs*10). Variants in the VLDLR gene have been shown to cause congenital cerebellar ataxia and mental retardation in human patients and Vldlr knockout mice also display an ataxia phenotype. Our combined genetic data together with the functional knowledge on the VLDLR gene from other species thus strongly suggest that VLDLR:c.1713delC is indeed causing DWLM in Eurasier dogs.

Mycoplasma bovis infections in Swiss dairy cattle: a clinical investigation

Mycoplasma bovis causes mastitis in dairy cows and is associated with pneumonia and polyarthritis in cattle. The present investigation included a retrospective case–control study to identify potential herd-level risk factors for M. bovis associated disease, and a prospective cohort study to evaluate the course of clinical disease in M. bovis infected dairy cattle herds in Switzerland. Eighteen herds with confirmed M. bovis cases were visited twice within an average interval of 75 d. One control herd with no history of clinical mycoplasmosis, matched for herd size, was randomly selected within a 10 km range for each case herd. Animal health data, production data, information on milking and feeding-management, housing and presence of potential stress- factors were collected. Composite quarter milk samples were aseptically collected from all lactating cows and 5% of all animals within each herd were sampled by nasal swabs. Organ samples of culled diseased cows were collected when logistically possible. All samples were analyzed by real-time polymerase chain reaction (PCR). In case herds, incidence risk of pneumonia, arthritis and clinical mastitis prior to the first visit and incidence rates of clinical mastitis and clinical pneumonia between the two visits was estimated. Logistic regression was used to identify potential herd-level risk factors for M. bovis infection. In case herds, incidence risk of M. bovis mastitis prior to the first visit ranged from 2 to 15%, whereas 2 to 35% of the cows suffered from clinical pneumonia within the 12 months prior to the first herd visit. The incidence rates of mycoplasmal mastitis and clinical pneumonia between the two herd visits were low in case herds (0–0.1 per animal year at risk and 0.1-0.6 per animal year at risk, respectively). In the retrospective-case-control study high mean milk production, appropriate stimulation until milk-let-down, fore-stripping, animal movements (cattle shows and trade), presence of stress-factors, and use of a specific brand of milking equipment, were identified as potential herd-level risk factors. The prospective cohort study revealed a decreased incidence of clinical disease within three months and prolonged colonization of the nasal cavity by M. bovis in young stock.

Long-term forest fire ecology and dynamics in southern Switzerland

1 Pollen and charcoal analysis at two lakes in southern Switzerland revealed that fire has had a prominent role in changing the woodland composition of this area for more than 7000 years. 2 The sediment of Lago di Origlio for the period between 5100 and 3100 bc cal. was sampled continuously with a time interval of about 10 years. Peaks of charcoal particles were significantly correlated with repeated declines in pollen of Abies, Hedera, Tilia, Ulmus, Fraxinus excelsior t., Fagus and Vitis and with increases in Alnus glutinosa t., shrubs (e.g. Corylus, Salix and Sambucus nigra t.) and several herbaceous species. The final disappearance of the lowland Abies alba stands at around 3150 bc cal. may be an example of a fire-caused local extinction of a fire-intolerant species. 3 Forest fires tended to diminish pollen diversity. The charcoal peaks were preceded by pollen types indicating human activity. Charcoal minima occurred during periods of cold humid climate, when fire susceptibility would be reduced. 4 An increase of forest fires at about 2100 bc cal. severely reduced the remaining fire-sensitive plants: the mixed-oak forest was replaced by a fire-tolerant alder–oak forest. The very strong increase of charcoal influx, and the marked presence of anthropogenic indicators, point to principally anthropogenic causes. 5 We suggest that without anthropogenic disturbances Abies alba would still form lowland forests together with various deciduous broadleaved tree taxa.

Time-order errors and standard-position effects in duration discrimination: An experimental study and an analysis by the sensation-weighting model

Studies have shown that the discriminability of successive time intervals depends on the presentation order of the standard (St) and the comparison (Co) stimuli. Also, this order affects the point of subjective equality. The first effect is here called the standard-position effect (SPE); the latter is known as the time-order error. In the present study, we investigated how these two effects vary across interval types and standard durations, using Hellström’s sensation-weighting model to describe the results and relate them to stimulus comparison mechanisms. In Experiment 1, four modes of interval presentation were used, factorially combining interval type (filled, empty) and sensory modality (auditory, visual). For each mode, two presentation orders (St–Co, Co–St) and two standard durations (100 ms, 1,000 ms) were used; half of the participants received correctness feedback, and half of them did not. The interstimulus interval was 900 ms. The SPEs were negative (i.e., a smaller difference limen for St–Co than for Co–St), except for the filled-auditory and empty-visual 100-ms standards, for which a positive effect was obtained. In Experiment 2, duration discrimination was investigated for filled auditory intervals with four standards between 100 and 1,000 ms, an interstimulus interval of 900 ms, and no feedback. Standard duration interacted with presentation order, here yielding SPEs that were negative for standards of 100 and 1,000 ms, but positive for 215 and 464 ms. Our findings indicate that the SPE can be positive as well as negative, depending on the interval type and standard duration, reflecting the relative weighting of the stimulus information, as is described by the sensation-weighting model.

MYELINATION IN UNDERNOURISHED RAT BRAIN

Several interactive parameters of protein-calorie malnutrition imposed during postnatal ontogeny on the myelination of rat brain wre investigated. Postnatal starvation depresses the rate of myelin protein synthesis to approximately the same extent in all major brain regions examined (cerebral cortex, cerebellum, striatum, hippocampus, hypothalamus, midbrain and medulla), indicating a relatively uniform reduction in myelination throughout the brain. Early starvation from birth through 8 days, as well as starvation occurring late, from 14 to 30 days, produced no lasting deficit in myelin accumulation. Starvation from birth through 14 days or from birth through 20 days produces lasting, significant myelin deficits in all brain regions when examined following ad libitum feeding to 60 days of age. These data, in combination with the metabolic studies of myelin synthesis, show that severe starvation occurring during the 2nd and 3rd weeks of postnatal life produces an immediate reduction in myelin synthesis, and that the subsequent deficit in myelin accumulation is irreversible by nutritional rehabilitation. With respect to the relative severity of nutritional restriction occurring during this "critical" interval of brain ontogeny, additional studies showed that mild undernourishment (producing less than 20 percent growth lag) produces no myelin deficit. There appears to be a threshold effect such that undernutrition producing a growth lag of between 20 to 30 percent first produces a measurable deficit. Increasingly severe regimens of nutritional restriction which produce approximately 30, 40 and 50 percent body weight lags result in initial myelin deficits of 25, 55 and 60 percent, respectively. Initial myelin deficits do not recover following nutritional rehabilitation, although myelin continues to increase in both normal and all undernourished populations. At the cellular level, severe postnatal nutritional restriction appears to depress both the initial synthesis of myelin precursor proteins (as demonstrated for proteolipid protein) as well as their subsequent assembly into myelin membrane. All of the findings of the present studies are consistent with a hypothetical model of undernutrition-induced brain hypomyelination in which the primary defect consists of a failure of oligodendroglia to myelinate a substantial percentage of axons, resulting in a greatly decreased ratio of myelinated to unmyelinated axons. ^

A novel myeloid leukemia suppressor locus at human chromosome 5q13.3

Molecular mechanisms that underlie preleukemic myelodysplasia (MDS) and acute myelogenous leukemia (AML) are poorly understood. In MDS or AML with a refractory clinical course, more than 30% of patients have acquired interstitial or complete deletions of chromosome 5. The 5q13.3 chromosomal segment is commonly lost as the result of 5q deletion. Reciprocal and unbalanced translocations of 5q13.3 can also occur as sole anomalies associated with refractory AML or MDS. This study addresses the hypothesis that a critical gene at 5q13.3 functions either as a classical tumor suppressor or as a chromosomal translocation partner and contributes to leukemogenesis. ^ Previous studies from our laboratory delineated a critical region of loss to a 2.5–3.0Mb interval at 5q13.3 between microsatellite markers D5S672 and GATA-P18104. The critical region of loss was later resolved to an interval of approximately 2Mb between the markers D5S672 and D5S2029. I, then generated a long range physical map of yeast artificial chromosomes (YACs) and developed novel sequence tagged sites (STS). To enhance the resolution of this map, bacterial artificial chromosomes (BACs) were used to construct a triply linked contig across a 1 Mb interval. These BACs were used as probes for fluorescent in situ hybridization (FISH) on an AML cell line to define the 5q13.3 critical region. A 200kb BAC, 484a9, spans the translocation breakpoint in this cell line. A novel gene, SSDP2 (single stranded DNA binding protein), is disrupted at the breakpoint because its first four exons are encoded within 140kb of BAC 484a9. This finding suggests that SSDP2 is the critical gene at 5q13.3. ^ In addition, I made an observation that deletions of chromosome 5q13 co-segregate with loss of the chromosome 17p. In some cases the deletions result from unbalanced translocations between 5q13 and 17p13. It was confirmed that the TP53 gene is deleted in patients with 17p loss, and the remaining allele harbors somatic mutation. Thus, the genetic basis for the aggressive clinical course in AML and MDS may be caused by functional cooperation between deletion or disruption of the 5q13.3 critical gene and inactivation of TP53. ^

Forebrain-cerebellum interactions revealed by trace eyelid conditioning

While it is commonly assumed that brain systems receive and process information from other brain systems, there are few examples of tractable behaviors that allow such interactions to be studied. With the experiments presented in this dissertation we provide evidence that trace eyelid conditioning, a simple form of associative learning, is mediated by cerebellar learning in response to the output of persistent neural activity in the prefrontal cortex (PFC) and thus may be useful in analyses of PFC-cerebellar interactions. In a series of stimulation and reversible inactivation experiments we provide evidence that trace eyelid conditioning is mediated by cerebellar learning in response to a learned forebrain-driven input. Specifically, we provide evidence that this input is driven by the medial PFC and persists through the stimulus free trace interval of trace eyelid conditioning. In the next set of experiments we show that directly presenting the cerebellum with a pattern of input that mimics the classic persistent activity of PFC neurons reconstitutes trace eyelid conditioning, as assessed by a number of stringent tests. Finally, in set of reversible inactivation experiments, we provide evidence that bidirectional learning during trace eyelid conditioning involves the omission of the persistent, PFC-driven input that the cerebellum learns and responds to during trace eyelid conditioning. Given that persistent activity in PFC is often associated with working memory, these experiments suggest that trace eyelid conditioning may be useful in analyses of working memory mechanisms, cerebellar information processing and their interaction. To facilitate future analyses, we conclude with a working hypothesis of forebrain-cerebellum interactions during trace eyelid conditioning that addresses how persistent activity in PFC is induced and how the cerebellum decodes and uses PFC-driven input. ^

Secondary left ventricular ejection fraction response to beta blocker therapy in heart failure patients

Chronic β-blocker treatment improves survival and left ventricular ejection fraction (LVEF) in patients with systolic heart failure (HF). Data on whether the improvement in LVEF after β-blocker therapy is sustained for a long term or whether there is a loss in LVEF after an initial gain is not known. Our study sought to determine the prevalence and prognostic role of secondary decline in LVEF in chronic systolic HF patients on β-blocker therapy and characterize these patients. Retrospective chart review of HF hospitalizations fulfilling Framingham Criteria was performed at the MEDVAMC between April 2000 and June 2006. Follow up vital status and recurrent hospitalizations were ascertained until May 2010. Three groups of patients were identified based on LVEF response to beta blockers; group A with secondary decline in LVEF following an initial increase, group B with progressive increase in LVEF and group C with progressive decline in LVEF. Covariate adjusted Cox proportional hazard models were used to examine differences in heart failure re-hospitalizations and all cause mortality between the groups. Twenty five percent (n=27) of patients had a secondary decline in LVEF following an initial gain. The baseline, peak and final LVEF in this group were 27.6±12%, 40.1±14% and 27.4±13% respectively. The mean nadir LVEF after decline was 27.4±13% and this decline occurred at a mean interval of 2.8±1.9 years from the day of beta blocker initiation. These patients were older, more likely to be whites, had advanced heart failure (NYHA class III/IV) more due to a non ischemic etiology compared to groups B & C. They were also more likely to be treated with metoprolol (p=0.03) compared to the other two groups. No significant differences were observed in combined risk of all cause mortality and HF re-hospitalization [hazard ratio 0.80, 95% CI 0.47 to 1.38, p=0.42]. No significant difference was observed in survival estimates between the groups. In conclusion, a late decline in LVEF does occur in a significant proportion of heart failure patients treated with beta blockers, more so in patients treated with metoprolol.^

Facies investigations on sediment core CRP-3 from the Ross Sea, Antarctica

The Cenozoic Victoria Land Basin (VLB) stratigraphic section penetrated by CRP-3 is mostly of Early Oligocene age. It contains an array of lithofacies comprising fine-grained mudrocks, interlaminated and interbedded mudrocks/sandstones, mud-rich and mud-poor sandstones, conglomerates and diamctites that are together interpreted as the products of shallow marine to possibly non-marine environments of deposition, affected by the periodic advance and retreat of tidewater glaciers. This lithofacies assemblage can be readily rationalised using the facies scheme designed originally for CRP-2/2A, and published previously. The uppermost 330 metres below sea floor (mbsf) shows a cyclical arrangement of lithofacies also similar to that recognised throughout CRP-2/2A, and interpreted to reflect cyclical variations in relative sea-level driven by ice volume fluctuations ('Motif A'). Between 330 and 480 mbsf, a series of less clearly cyclical units, generally fining-upward but nonetheless incorporating a significant subset of the facies assemblage, has been identified and noted in the Initial Report as 'Motif B' Below 480 mbsf, the section is arranged into a repetitive succession of fining-upward units, each of which comprises dolerite clast conglomerate at the base passing upward into relatively thick intervals of sandstones. The cycles present down 480 mbsf are defined as sequences, each interpreted to record cyclical variation of relative sea-level. The thickness distribution of sequences in CRP-3 provides some insights into the geological variables controlling sediment accumulation in the Early Oligocene section. The uppermost part of the section in CRP-3 comprises two or three thick, complete sequences that show a broadly symmetrical arrangement of lithofacies (similar to Sequences 9-11 in CRP-2/2A). This suggests a period of relatively rapid tectonic subsidence, which allowed preservation of the complete facies cycle. Below Sequence 3, however, is a considerable interval of thin, incomplete and erosionally truncated sequences (4-23), which incorporates both the remainder of Motif A sequences and all Motif B sequences recognised. The thinner and more truncated sequences suggest sediment accumulation under conditions of reduced accommodation, and given the lack of evidence for glacial conditions (see Powell et al., this volume) tends to argue for a period of reduced tectonic subsidence. The section below 480 mbsf consists of a series of fining-upward, conglomerate to sandstone intervals which cannot be readily interpreted in terms of relative sea-level change. A relatively mudrock-rich interval above the basal conglomerate/breccia (782-762 mbsf) may record initial flooding of the basin during early rift subsidence. The lithostratigraphy summarised above has been linked to seismic reflection data using depth conversion techniques (Henrys et al., this volume). The three uppermost reflectors ('o', 'p' and 'q') correlate to the package of thick sequences 1-3, and several deeper reflectors can also be correlated to sequence boundaries. The package of thick Sequences 1-3 shows a sheet-like cross-sectional geometry on seismic reflection lines, unlike the similar package recognised in CRP-2/2A.

The Cenomanian/Turronian Boundary Event at ODP Hole 103-641A

Drilling at ODP Site 641 (on the western margin of Galicia Bank, off northwestern Spain) revealed a thin, but pronounced, interval of black shale and gray-green claystone. Our high-resolution study combines the sedimentology, micropaleontology (palynomorphs and others), organic and inorganic geochemistry, and isotopic values of this layer to demonstrate the distinct nature of the sediment and prove that the sequence represents the local sedimentary expression of the global Cenomanian/Turonian Oceanic Anoxic Event (OAE) of Schlanger and Jenkyns (1976), Arthur and Schlanger (1979), and Jenkyns (1980), also called the Cenomanian/Turonian Boundary Event (CTBE). The most striking evidence is that the strong positive d13C excursion characterizing the CTBE sequences in shallow areas can be traced into a pronounced deep-sea expression, thus providing a good stratigraphic marker for the CTBE in various paleosettings. The isotopic excursion at Site 641 coincides with an extremely enriched trace metal content, with values that were previously unknown for the Cretaceous Atlantic. Similar to other CTBE occurrences, the organic carbon content is high (up to 11%) and the organic matter is of dominantly marine origin (kerogen type II). The bulk mineralogy of the CTBE sediments does not differ significantly from the general trend of Cretaceous North Atlantic sediments (dominance of smectite and zeolite with minor amounts of illite and scattered palygorskite, kaolinite, and chlorite); thus, no evidence for either increased volcanic activity nor a drastic climatic change in the borderlands was found. Results from Site 641 are compared with the CTBE section found at Site 398, DSDP Leg 47B (Vigo Seamount at the southern end of the Galicia Bank).

Geochemistry and mineralogy at DSDP Holes 61-462, 61-462A and 33-315A

Sedimentary rocks of Barremian through early Maestrichtian age recovered on Deep Sea Drilling Project Leg 61 had their principal source in the complex of igneous rocks with which they are interlayered in the Nauru Basin. Relict textures and primary sedimentary structures show these Cretaceous sediments to be of hyaloclastic origin, in part reworked and redeposited by slumps and currents. The dominant composition now is smectite, but locally iron, titanium, and manganese oxides, plagioclase, pyroxene, analcime, clinoptilolite, chalcedonic quartz, cristobalite, amphibole, nontronite, celadonite, and pyrite are also present. The mineral assemblages and the geochemistry reflect the original basaltic composition and its subsequent alteration by one or more processes of submarine weathering, authigenesis, hydrothermal circulation, and contact metamorphism. Hyaloclastitic sandstone, siltstone, and breccia within the sheet flows below 729 meters sub-bottom depth have Barremian fossils, thus establishing the age of the lower, or extrusive, complex of post-ridge-crest volcanism. Similar hyaloclastites between 564 and 729 meters are invaded by hypabyssal sills of the upper igneous complex, and fossil ages of Albian or Cenomanian set an older limit to the age of that second post-ridge-crest episode. Cenomanian to early Campanian sedimentary rocks between 490 and 564 meters have a substantial contribution of clays of submarine-weathered-basalt origin, as well as hydrothermal and pelagic components. The interval of reworked hyaloclastitic siltstone, sandstone, and breccias between 450 and 490 meters is of late Campanian and early Maestrichtian age. These sediments probably formed from glassy basalt that fragmented upon eruption nearby, when sills were being emplaced. In addition to pelagic elements, these Upper Cretaceous volcanogenic sediments include redeposited material of shallow-water origin, apparently derived from the Marshall Islands.

Silicoflagellates and ebridians from the New Jersey Transect DSDP Leg 93

Well-preserved and diverse silicoflagellate and ebridian populations are found in the lower and middle Eocene sediments of DSDP Site 605 and the upper Miocene sediments of DSDP Site 604. The ebridians outnumber the silicoflagellates in the siliceous interval of Site 605, but are less numerous at Site 604. The abundances of the various taxa are tabulated.

Age models and stable isotope ratios from the Mid-Miocene

Mid-Miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera. Precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates, for example, Deep Sea Drilling Project sites 289 and 574. The mid-Miocene carbon isotope records are characterized by an interval of high d13C values between 17 and 13.5 Ma (the Monterey Excursion of Vincent and Berger 1985) upon which are superimposed a series of periodic or quasi-periodic fluctuations in d13C values. These fluctuations have a period of approximately 440 kyr, suggestive of the 413 kyr cycle predicted by Milankovitch theory. Vincent and Berger proposed that the Monterey Excursion was the result of increased organic carbon burial in continental margins sediments. The increased d13C values (called 13C maxima) superimposed on the generally high mid-Miocene signal coincide with increases in d18O values suggesting that periods of cooling and/or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric CO2 levels. It is likely that during the Monterey Excursion the ocean/atmosphere system became progressively more sensitive to small changes in insolation, ultimately leading to major cooling of deep water and expansion of continental ice. We have assigned an absolute chronology, based on biostratigraphic and magneto-biostratigraphic datum levels, to the isotope stratigraphy and have used that chronology to correlate unconformities, seismic reflectors, carbonate minima, and dissolution intervals. Intervals of sediment containing 13C maxima are usually better preserved than the overlying and underlying sediments, indicating that the d13C values of TCO2 in deep water and the corrosiveness of seawater are inversely correlated. This again suggests that the 13C maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric CO2. The absolute chronology we have assigned to the isotopic record indicates that the major mid-Miocene deepwater cooling/ice volume expansion took 2 m.y. and was not abrupt as had been reported previously. The cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals. The cooling was not monotonic, and the 2 m.y. interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period. The increase in d18O values of benthic foraminifera between 14.9 and 12.9 Ma was greatest at deeper water sites and at sites closest to Antarctica. The data suggest that the d18O value of seawater increased by no more than about 1.1 per mil during this interval and that the remainder of the change in benthic d18O values resulted from cooling in Antarctic regions of deepwater formation. Equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0.4 per mil steplike increases in d13C values. Only one of these increases in planktonic d13C is correlated with any of the features in the mid-Miocene benthic carbon isotope record.

Reseña sobre las metodologías de campo, analíticas y estadísticas empleadas en la determinación y manejo de datos de los elementos de tierras raras en el sistema suelo-planta

El presente artículo es una revisión detallada de estudios científicos publicados que tratan el tema relacionado con la determinación de los elementos de las tierras raras (REEs) en el sistema suelo-planta. Los estudios han sido llevados a cabo principalmente en países europeos y asiáticos. Cabe señalar que la investigación en los países latinoamericanos es muy escasa; sin embargo, es creciente el interés de analizar la aportación de estos elementos al suelo y la planta, lo cual se debe a la aplicación de fertilizantes que contienen dosis elevadas de estos elementos en su composición. Diversas técnicas de muestreo, experimentación y análisis han sido empleadas para la determinación de los REEs. No obstante, se considera que el manejo de los datos ha sido incorrecto estadísticamente. El contenido del presente artículo aborda: (i) las generalidades de los REEs; (ii) el análisis de la bibliografía disponible con el fin de conocer las metodologías de muestreo y análisis más utilizadas en 37 artículos en total, señalando algunos puntos que se consideran todavía deficientes; (iii) dos ejemplos de la aplicación de técnicas estadísticas (intervalo de confianza de la media y pruebas de significancia de la relación F de Fisher y t de Student) utilizando datos reportados en dos artículos. Los resultados mostraron, con los datos del primer artículo analizado, que: a) no se aplicó una metodología estadística para evaluar la calidad de datos; b) al aplicar estadística se encontró que existen diferencias sistemáticas entre los datos determinados en el laboratorio y los certificados. En el segundo artículo analizado se demostró, mediante pruebas de significancia, que existen diferencias significativas en las medias de Ce y Eu (los dos elementos tomados como ejemplos) en las plantas de un sitio a otro.