Searchlight New Mexico interviews Maryam Ahranjani on the Prisonization of America\u27s Public Schools

Maryam Ahranjani writes about personal experiences with mass school shootings in The Prisonization of America\u27s Public Schools, published in October 2017 in Hofstra Law Review. The article takes a critical stance against what Ahranjani terms the growing criminal infrastructure metal detectors, surveillance cameras and police officers within our nation\u27s schools. Searchlight New Mexico asked Ahranjani what kind of national response makes sense in the wake of the Parkland mass shooting

Continuum-based models and concepts for the transport of nanoparticles in saturated porous media: A state-of-the-science review

Environmental applications of nanoparticles (NP) increasingly result in widespread NP distribution within porous media where they are subject to various concurrent transport mechanisms including irreversible deposition, attachment/detachment (equilibrium or kinetic), agglomeration, physical straining, site-blocking, ripening, and size exclusion. Fundamental research in NP transport is typically conducted at small scale, and theoretical mechanistic modeling of particle transport in porous media faces challenges when considering the simultaneous effects of transport mechanisms. Continuum modeling approaches, in contrast, are scalable across various scales ranging from column experiments to aquifer. They have also been able to successfully describe the simultaneous occurrence of various transport mechanisms of NP in porous media such as blocking/straining or agglomeration/deposition/detachment. However, the diversity of model equations developed by different authors and the lack of effective approaches for their validation present obstacles to the successful robust application of these models for describing or predicting NP transport phenomena. This review aims to describe consistently all the important NP transport mechanisms along with their representative mathematical continuum models as found in the current scientific literature. Detailed characterizations of each transport phenomenon in regards to their manifestation in the column experiment outcomes, i.e., breakthrough curve (BTC) and residual concentration profile (RCP), are presented to facilitate future interpretations of BTCs and RCPs. The review highlights two NP transport mechanisms, agglomeration and size exclusion, which are potentially of great importance in controlling the fate and transport of NP in the subsurface media yet have been widely neglected in many existing modeling studies. A critical limitation of the continuum modeling approach is the number of parameters used upon application to larger scales and when a series of transport mechanisms are involved. We investigate the use of simplifying assumptions, such as the equilibrium assumption, in modeling the attachment/detachment mechanisms within a continuum modelling framework. While acknowledging criticisms about the use of this assumption for NP deposition on a mechanistic (process) basis, we found that its use as a description of dynamic deposition behavior in a continuum model yields broadly similar results to those arising from a kinetic model. Furthermore, we show that in two dimensional (2-D) continuum models the modeling efficiency based on the Akaike information criterion (AIC) is enhanced for equilibrium vs kinetic with no significant reduction in model performance. This is because fewer parameters are needed for the equilibrium model compared to the kinetic model. Two major transport regimes are identified in the transport of NP within porous media. The first regime is characterized by higher particle-surface attachment affinity than particle-particle attachment affinity, and operative transport mechanisms of physicochemical filtration, blocking, and physical retention. The second regime is characterized by the domination of particle-particle attachment tendency over particle-surface affinity. In this regime although physicochemical filtration as well as straining may still be operative, ripening is predominant together with agglomeration and further subsequent retention. In both regimes careful assessment of NP fate and transport is necessary since certain combinations of concurrent transport phenomena leading to large migration distances are possible in either case

Comparative kinetic desorption of 60Co, 85Sr and 134Cs from a contaminated natural silica sand column: Influence of varying physicochemical conditions and dissolved organic matter

In order to determine the mechanisms of the retention of 60Co, 85Sr and 134Cs in natural silica sand columns, desorption experiments were performed by changes of pH and ionic strength and by injection of natural organic matter (NOM). Injection of KCl (0.1 M) resulted in a high release of 60Co (60-100%) and 85Sr (72-100%) but a smaller release of 134Cs (31-66%). Only limited release of 60Co (66%) and 85Sr (71%) and no release of 134Cs were observed by injection of NOM. The different percentages of desorption were related to the chemical characteristics of the organic colloids previously retained in columns before the desorption step. The results evidenced different sorption processes on energetically heterogeneous surface sites. According to the initial conditions, the binding of the radionuclides to the solid phase resulted from weak and easily reversible sorption processes to strong association probably by inner sphere complexes. The rather weak release of 134Cs by KCl was attributed to the strong retention of 134Cs by clay coatings on the natural silica sand surfaces. © 2005 Elsevier Ltd. All rights reserved

Interactions between two types of nanoparticles (nC(60) and TiO2) and porous media

19th Annual VM Goldschmidt Conference, Davos, SWITZERLAND, JUN 21, 2009International audienceno abstrac

Influence de la phase colloïdale sur le transfert des radionucleides en milieux poreux

Jusqu'à présent, l'influence des paramètres physico-chimiques du milieu sur le transfert de radioéléments en présence de colloïdes a été peu abordé, alors que les colloïdes peuvent changer significativement le transfert de REs. Les interactions entre les colloïdes (polymères hydrophiles, polymères hydrophobes, matière organique (MO)), les REs (134Cs, 85Sr, 60Co) et la phase solide (sable silicieux) ont été étudiées par des expériences en batch et en colonne. Ce travail met en évidence l'importance de la phase colloïdale sur le transfert de REs en milieu poreux. On observe que quelque soit la nature de colloïdes, les colloïdes peuvent accélérer ou retarder le transfert de REs. La présence de la MO change plus significativement le transfert des REs étudiés par rapport aux polymères synthétiques. Nous avons développé un modèle pour décrire le transfert de REs en milieu poreux en prenants en compte des interactions entre les REs et la matrice par des processus instantanés et non instantanés.AIX-MARSEILLE3-BU Sc.St Jérô (130552102) / SudocSudocFranceF

Influence of the colloid type on the transfer of 60Co and 85Sr in silica sand column under varying physicochemical conditions

The influence of two types of colloids (natural organic matter, NOM), a colloid with high affinity for radionuclides (RN(s)), and hydrophilic synthetic latex (SHL), a colloid with low affinity for RN(s) on the transfer of 60Co and 85Sr in a silica sand column was studied under different physicochemical conditions : pH (4.9), ionic strength (10-3 M and 10-2 M), concentration of colloids (100 mg l-1, 10 mg l-1), flow velocity (12.4 cm h-1 and 3.7 cm h-1), water saturation of the column (100% and 70%). In the absence of colloids, the transfer of 60Co and 85Sr was retarded compared to the transfer of the conservative tracer. In the presence of colloids and according to the specific physicochemical conditions, an acceleration or retardation of 60Co and 85Sr transfer was observed compared to their transfer in the absence of colloids. Our results evidenced that any colloids even with low reactivity could significantly modify the RN transfer. However, the extent to which the transfer was influenced differs according to the colloid type; the NOM exhibiting higher impact than SHL. Batch experiments helped in interpreting of the interactions between the colloids, RN(s) and solid phase observed in column. © 2006 Elsevier Ltd. All rights reserved

Comparative behaviour of recently deposited radiostrontium and atmospheric common strontium in soils (Vosges mountains, France).

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