Sit down at the ball game: how trade barriers make the world less food secure

This paper analyses the impacts of trade policy responses to rising world food prices by carrying out a series of stylised experiments in the wheat market using a world trade model, GTAP. The sequence of events that is modelled comprises a negative wheat supply shock and subsequent implementation of an export tax by a major net exporter and a reduction in import tariffs by a small importer. The effects of trade policy responses are contrasted with those of full liberalisation of the wheat market. At the core are the (opposite) effects on producers and consumers, as well as the terms-of-trade and trade tax revenue effects. Food security is shown to depend crucially on changes in prices but also in incomes that are associated with changes in factor returns. The results reveal that major net exporters are generally better off when implementing export taxes for food security purposes. Large exporting countries export price instability causing world food prices to rise further. Net importing countries lose out and have limited leeway to reduce tariffs or subsidise imports. Liberalising wheat trade mitigates rising prices and contributes to food security, but to the detriment of production in Africa and Asia, making them more dependent on and vulnerable to changes in the world market. Concerted action at the WTO forum is required, notably clarifying and sharpening the rules regarding export measures.food security; world food crisis; international grain trade; trade measures; trade liberalisation; CGE modelling

The Quiet-Sun Photosphere and Chromosphere

The overall structure and the fine structure of the solar photosphere outside active regions are largely understood, except possibly important roles of a turbulent near-surface dynamo at its bottom, internal gravity waves at its top, and small-scale vorticity. Classical 1D static radiation-escape modelling has been replaced by 3D time-dependent MHD simulations that come closer to reality. The solar chromosphere, in contrast, remains ill-understood although its pivotal role in coronal mass and energy loading makes it a principal research area. Its fine structure defines its overall structure, so that hard-to-observe and hard-to-model small-scale dynamical processes are the key to understanding. However, both chromospheric observation and chromospheric simulation presently mature towards the required sophistication. The open-field features seem of greater interest than the easier-to-see closed-field features.Comment: Accepted for special issue "Astrophysical Processes on the Sun" of Phil. Trans. Royal Soc. A, ed. C. Parnell. Note: clicking on the year in a citation opens the corresponding ADS abstract page in the browse

Convective Dynamos and the Minimum X-ray Flux in Main Sequence Stars

The objective of this paper is to investigate whether a convective dynamo can account quantitatively for the observed lower limit of X-ray surface flux in solar-type main sequence stars. Our approach is to use 3D numerical simulations of a turbulent dynamo driven by convection to characterize the dynamic behavior, magnetic field strengths, and filling factors in a non-rotating stratified medium, and to predict these magnetic properties at the surface of cool stars. We use simple applications of stellar structure theory for the convective envelopes of main-sequence stars to scale our simulations to the outer layers of stars in the F0--M0 spectral range, which allows us to estimate the unsigned magnetic flux on the surface of non-rotating reference stars. With these estimates we use the recent results of \citet{Pevtsov03} to predict the level of X-ray emission from such a turbulent dynamo, and find that our results compare well with observed lower limits of surface X-ray flux. If we scale our predicted X-ray fluxes to \ion{Mg}{2} fluxes we also find good agreement with the observed lower limit of chromospheric emission in K dwarfs. This suggests that dynamo action from a convecting, non-rotating plasma is a viable alternative to acoustic heating models as an explanation for the basal emission level seen in chromospheric, transition region, and coronal diagnostics from late-type stars.Comment: ApJ, accepted, 30 pages with 7 figure

Ca II H and K Chromospheric Emission Lines in Late K and M Dwarfs

We have measured the profiles of the Ca II H and K chromospheric emission lines in 147 main sequence stars of spectral type M5-K7 (0.30-0.55 solar masses) using multiple high resolution spectra obtained during six years with the HIRES spectrometer on the Keck 1 telescope. Remarkably, the average FWHM, equivalent widths, and line luminosities of Ca II H and K increase by a factor of 3 with increasing stellar mass over this small range of stellar masses. We fit the H and K lines with a double Gaussian model to represent both the chromospheric emission and the non-LTE central absorption. Most of the sample stars display a central absorption that is typically redshifted by ~0.1 km/s relative to the emission, but the nature of this velocity gradient remains unknown. The FWHM of the H and K lines increase with stellar luminosity, reminiscent of the Wilson-Bappu effect in FGK-type stars. Both the equivalent widths and FWHM exhibit modest temporal variability in individual stars. At a given value of M_v, stars exhibit a spread in both the equivalent width and FWHM of Ca II H and K, due both to a spread in fundamental stellar parameters including rotation rate, age, and possibly metallicity, and to the spread in stellar mass at a given M_v. The K line is consistently wider than the H line, as expected, and its central absorption is more redshifted, indicating that the H and K lines form at slightly different heights in the chromosphere where the velocities are slightly different. The equivalent width of H-alpha correlates with Ca II H and K only for stars having Ca II equivalent widths above ~2 angstroms, suggesting the existence of a magnetic threshold above which the lower and upper chromospheres become thermally coupled.Comment: 40 pages including 12 figures and 17 pages of tables, accepted for publication in PAS

Addendum: "The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models" (ApJ, 481, 267 [1997])

It has recently come to our attention that there are axis scale errors in three of the figures of Dull et al. (1997, hereafter D97). D97 presented Fokker-Planck models for the collapsed-core globular cluster M15 that include a dense, centrally concentrated population of neutron stars and massive white dwarfs, but do not include a central black hole. In this Addendum, we present corrected versions of Figures 9, 10, and 12, and an expanded version of Figure 6. This latter figure, which shows the full run of the velocity dispersion profile, indicates that the D97 model predictions are in good agreement with the moderately rising HST-STIS velocity dispersion profile for M15 reported by Gerssen et al. (2002, astro-ph/0209315). Thus, a central black hole is not required to fit the new STIS velocity measurements, provided that there is a sufficient population of neutron stars and massive white dwarfs. This conclusion is consistent with the findings of Gerssen et al. (2002, astro-ph/0210158), based on a reapplication of their Jeans equation analysis using the corrected mass-to-light profile (Figure 12) for the D97 models.Comment: 4 pages, 4 figures, submitted to Ap

Perioperative executive functioning in patients with low-grade gliomas near the Frontal Aslant Tract

Background A tract potentially involved in important executive cognitive processes is the Frontal Aslant Tract (FAT). In particular the right FAT has been associated with executive functioning (EF). In neurosurgery, it remains unclear if patients with tumors near the FAT demonstrate EF impairments after resection. This study investigated whether low grade gliomas (LGG) that affect the core white matter and/or structural integrity of the FAT predict preoperative and 3 months postoperative EF, when controlled for tumor volume and the integrity of other nearby tracts (SLF II and SLF III). Material and Methods Data was analyzed from patients with frontal and parietal LGG who underwent surgery between 2010-2021. Probabilistic tractography was performed prior to surgery to generate preoperative tracts of the FAT, SLF II and SLF III. The core of the FAT was defined as the white matter between the seed and the target region. Average mean diffusivity for each tract was taken as a measure of structural integrity. EF was assessed one day before and 3 months post-surgery with the following tests: Stroop test, symbol digit coding test (SDC), shifting attention test (SAT), and letter fluency test (LF). We performed linear mixed models and linear regression analyses to investigate the relationship between presurgical tumor overlap with the core of the FAT and FAT integrity with pre- and postsurgical executive test performances. Results Seventy-five patients were included (left tumor N=39, right tumor N=36). Mean pre-surgical Z-scores were within 0.5 standard deviation from a healthy control group for all tests, but with substantial variance between patients (Z-score range:-3.59 to 2.4). The results demonstrated that core overlap of the right FAT predicted preoperative performance on the SAT (p<.01, β= -.473), Stroop (p<.01, β= -.519), and SDC (p<.01, β= -.519). Right or left core overlap did not significantly predict performance three months after surgery. FAT integrity did not predict preoperative EF performance, whereas it did predict SAT performance at three months post-surgical (p<.01, β= -.694) when controlled for SLF II, III integrity and tumor volume. Conclusion Although patients with frontal or parietal LGG showed no dysfunction on tests of EF before surgery on group level, they demonstrated large variability between patients. Tumor overlap with the core of the right FAT predicted worse presurgical EF performances, but not short-term post-surgical performances. Right FAT integrity predicted short-term post-surgical performance on cognitive flexibility. These results are in line with previous findings that the right FAT is involved in EF and indicate that preoperative FAT integrity might predict which patients will perform worse after surgery

Locally recurrent rectal cancer and distant metastases:is there still a chance ofcure?

Introduction: Patients with locally recurrent rectal cancer (LRRC) generally have poor prognosis, especially those who have (a history of) distant metastases. The aim of this study was to investigate the impact of distant metastases on oncological outcomes in LRRC patients undergoing curative treatment. Methods: Consecutive patients with surgically treated LRRC between 2005 and 2019 in two tertiary referral hospitals were retrospectively analysed. Oncological survival of patients without distant metastases were compared with outcomes of patients with synchronous distant metastases with the primary tumour, patients with distant metastases in the primary-recurrence interval, and patients with synchronous LRRC distant metastases. Results: A total of 535 LRRC patients were analysed, of whom 398 (74%) had no (history of) metastases, 22 (4%) had synchronous metastases with the primary tumour, 44 (8%) had metachronous metastases, and 71 (13%) had synchronous LRRC metastases. Patients with synchronous LRRC metastases had worse survival compared to patients without metastases (adjusted hazard ratio: 1.56 [1.15–2.12]), whilst survival of patients with synchronous primary metastases and metachronous metastases of the primary tumour was similar as those patients who had no metastases. In LRRC patients who had metastases in primary-recurrence interval, patients with early metachronous metastases had better disease-free survival as patients with late metachronous metastases (3-year disease-free survival: 48% vs 22%, p = 0.039). Conclusion: LRRC patients with synchronous distant metastases undergoing curative surgery have relatively poor prognosis. However, LRRC patients with a history of distant metastases diagnosed nearby the primary tumour have comparable (oncological) survival as LRRC patients without distant metastases.</p

A Systematic Investigation on the Hemalog

Peer Reviewe

Fully automatic meningioma segmentation using T1-weighted contrast-enhanced MR images only

Background Manual segmentation of brain tumors requires expertise, is time-consuming, and is subject to inter-rater variability. Fully automatic brain tumor segmentation is possible for glioma and meningioma when volumetric T1, T1 contrast-enhanced (T1c), T2, and Fluid-attenuated inversion recovery (FLAIR) MRIs are available. In clinical care of meningiomas, however, often only volumetric T1c scans are available. In this work, we trained a deep learning network to segment meningiomas using only T1c scans for use in clinical research. Material and Methods NnU-Net, a deep learning model that is optimized for medical image segmentation, was trained to segment meningiomas from T1c images. This was performed on a large clinically collected meningioma dataset (n=374) of T1c scans with semi-automatically generated enhancing tumor masks and additional data from the BraTS2020 glioma dataset. Model performance was compared against inter-rater reliability, between different models, between anatomical tumor locations, and against models using multiple MRI modalities. Results The best performing model obtained a Dice score of 0.90. This performance was 0.03 points lower when compared to inter-rater reliability (Dice=0.93) and almost equal to models using multiple MRI modalities. Model performance split over anatomical tumor locations was between 0.90 and 0.97 (Dice). Conclusion Fully automatic meningioma segmentation using only T1c images is possible with an accuracy that is similar to inter-rater reliability and models using multiple imaging modalities

Sit down at the ball game: how trade barriers make the world less food secure

This paper analyses the impacts of trade policy responses to rising world food prices by carrying out a series of stylised experiments in the wheat market using a world trade model, GTAP. The sequence of events that is modelled comprises a negative wheat supply shock and subsequent implementation of an export tax by a major net exporter and a reduction in import tariffs by a small importer. The effects of trade policy responses are contrasted with those of full liberalisation of the wheat market. At the core are the (opposite) effects on producers and consumers, as well as the terms-of-trade and trade tax revenue effects. Food security is shown to depend crucially on changes in prices but also in incomes that are associated with changes in factor returns. The results reveal that major net exporters are generally better off when implementing export taxes for food security purposes. Large exporting countries export price instability causing world food prices to rise further. Net importing countries lose out and have limited leeway to reduce tariffs or subsidise imports. Liberalising wheat trade mitigates rising prices and contributes to food security, but to the detriment of production in Africa and Asia, making them more dependent on and vulnerable to changes in the world market. Concerted action at the WTO forum is required, notably clarifying and sharpening the rules regarding export measures