Optics in Africa: introduction.

Africa has a long history in optics, but decades of turmoil have seen optical science in Africa advance only slowly, punching far below its weight. But a younger generation of scientists hold promise for the brighter future, addressing continental issues with photonics. In this Feature Issue on Optics in Africa we capture some of the exciting optical research from across the continent in 51 research reports, covering both fundamental and applied topics. The issue is supplemented by invited review articles that offer authoritative perspectives on the historical development of key research fields, from early advances in lasers to present-day progress in photonic materials. To encourage the exploration of new research directions, the issue has several tutorial articles that lower the entry barrier for emerging researchers, while highlighting the scope of research on the continent and its international context.

Dual-energy X-ray absorptiometry underestimates in vivo lumbar spine bone mineral density in overweight rats.

Dual-energy X-ray absorptiometry (DXA) is currently the most widely used technique for measuring areal bone mineral density (BMD). However, several studies have shown inaccuracy, with either overestimation or underestimation of DXA BMD measurements in the case of overweight or obese individuals. We have designed an overweight rat model based on junk food to compare the effect of obesity on in vivo and ex vivo BMD and bone mineral content measurements. Thirty-eight 6-month old male rats were given a chow diet (n = 13) or a high fat and sucrose diet (n = 25), with the calorie amount being kept the same in the two groups, for 19 weeks. L1 BMD, L1 bone mineral content, amount of abdominal fat, and amount of abdominal lean were obtained from in vivo DXA scan. Ex vivo L1 BMD was also measured. A difference between in vivo and ex vivo DXA BMD measurements (P < 0.0001) is evidenced with an underestimation of in vivo BMD by (8.47 ± 10.54)%. This difference was found for the chow and high fat, high sucrose diets (P = 0.008), and a significant interaction between in vivo measurements, ex vivo measurements, and diet was observed (P = 0.030). Also, the data show a positive significant correlation of ex vivo BMD with body weight, perirenal fat, abdominal fat, and abdominal lean. Multiple linear regression analysis shows that body weight, abdominal fat, and abdominal lean were independently related to ex vivo BMD. DXA underestimated lumbar in vivo BMD in overweight rats, and this measurement error is related to body weight and abdominal fat. Therefore, caution must be used when one is interpreting BMD among overweight and obese individuals.

Positive Association of Obesity and Insulin Resistance With Bone Mineral Density in Tunisian Postmenopausal Women.

The association of bone mineral density (BMD) with obesity and insulin resistance remains unclear. This study aimed to explore these associations in Tunisian menopausal women. Eighty-one postmenopausal women were recruited. Data were analyzed for obese (N = 57) and non-obese women (N = 24) and for insulin-resistant (N = 43) and non insulin-resistant women (N = 36). Anthropometric and biochemical parameters were recorded. BMD in different sites and body composition were measured using dual-energy X-ray absorptiometry. Higher BMD was observed in obese women than those non-obese in the left femur (p = 0.0067), right femur (p = 0.0108), total hip (p = 0.0077), and the whole body (p = 0.0276). Also BMD was significantly greater in insulin-resistant women than in non-insulin-resistant women when measured in the left femur and total hip. Positive correlations were recorded between BMD and anthropometric parameters, body composition parameters, and glycemia (r = 0.249, p < 0.05). Multiple linear regression analysis shows that only trunk fat (p < 0.05) and lean mass (p < 0.05) were independently and positively related to BMD, and the waist circumference was the only anthropometric parameter independently and negatively associated to BMD. BMD is improved in obese and insulin-resistant women. Also, trunk fat and lean mass are likely to be key positive independent factors for BMD.

Mid-infrared supercontinuum generation in multimode As2 Se3 chalcogenide photonic crystal fiber.

We rigorously investigated the mid-infrared supercontinuum generation in a multimode As2Se3 chalcogenide photonic crystal fiber (PCF). We studied the impact of the intermodal nonlinear effects on the nonlinear propagation of the fundamental and high-order modes. By solving the multimode generalized nonlinear Schrödinger equation, we have predicted the generation of a very broadband supercontinuum in both polarizations of the fundamental mode spanning from 2 to 11 µm at -20 dB in only 5 cm PCF length. The proposed study confirms that the energy transfer occurs only between the optical degenerate modes when propagating in the multimode chalcogenide PCF in the mid-infrared region.

Super-flat coherent supercontinuum source in As38.8Se61.2 chalcogenide photonic crystal fiber with all-normal dispersion engineering at a very low input energy.

We numerically report super-flat coherent mid-infrared supercontinuum (MIR-SC) generation in a chalcogenide As38.8Se61.2 photonic crystal fiber (PCF). The dispersion and nonlinear parameters of As38.8Se61.2 chalcogenide PCFs by varying the diameter of the air holes are engineered to obtain all-normal dispersion (ANDi) with high nonlinearities. We show that launching low-energy 50 fs optical pulses with 0.88 kW peak power (corresponding to pulse energy of 0.05 nJ) at a central wavelength of 3.7 µm into a 5 cm long ANDi-PCF generates a flat-top coherent MIR-SC spanning from 2900 to 4575 nm with a high spectral flatness of 3 dB. This ultra-wide and flattened spectrum has excellent stability and coherence properties that can be used for MIR applications such as medical diagnosis of diseases, atmospheric pollution monitoring, and drug detection.

Laparoscopic Pancreaticoduodenectomy with Reconstruction of the Portal Vein with the Parietal Peritoneum.

INTRODUCTION: Laparoscopic pancreaticoduodenectomy (LPD) is increasingly used for resections of periampullary tumors, including pancreatic adenocarcinoma.1 LPD with venous resection-reconstruction (VRR) has already been performed with or without vascular graft.2 (,) 3 The parietal peritoneum (PP) was recently described for reconstruction of the mesenterico-portal vein, with excellent results.4 PATIENTS AND METHODS: Between April 2011 and May 2015, a total of 64 LPDs were performed in our department; however, only one patient underwent VRR. Compared with the open approach, full mobilization of the mesentery and right liver is not systematically carried out and, theoretically, vascular grafts may be more frequently needed with LPD. In this video, LPD for pancreatic adenocarcinoma with resection of the lateral right side of the portal vein (>25 mm) was performed. Reconstruction was achieved rapidly, as a lateral patch, with the falciform ligament. RESULTS: Surgery lasted 360 min, 60 min of portal vein occlusion, 200 ml of blood loss, and uneventful stay. Since 2010, the PP has been used as a lateral patch in 69 patients operated by open (n = 68) or laparoscopic approach (n = 1). Although handling and suturing can be difficult, no bleeding complications related to the PP were observed and the permeability rate was >95 %. CONCLUSION: LPD is still restricted to selected centers, with conflicting results regarding safety; however, venous resection may be required. We feel that with the laparoscopic approach, vascular grafts are more frequently needed and the PP has many advantages compared with an open approach, including easy access, unlimited size, and rapid harvesting.

Rigorous study of supercontinuum generation in few mode fibers.

We numerically studied supercontinuum (SC) generation in a few-mode photonic crystal fiber (PCF). We have shown the impact of the intermodal nonlinear effects that could limit the fundamental mode nonlinear propagation due to the coupling induced by high-order optical modes. We have demonstrated an accurate modeling of the SC generation into the multimode PCF by solving the multimode generalized nonlinear Shrödinger equation (MM-GNLSE). Our detailed investigation of the dynamics of the intermodal nonlinear effects on the SC process confirms the energy transfer between optical degenerate modes during propagation inside the few-mode PCF.

Cytosinium hydrogen selenite.

In the crystal structure of the title salt, C4H6N3O(+)·HSeO3 (-), systematic name 6-amino-2-methyl-idene-2,3-di-hydro-pyrim-idin-1-ium hydrogen selenite, the hydrogenselenite anions and the cytosinium cations are linked via N-H⋯O, N-H⋯Se, O-H⋯O, O-H··Se and C-H⋯O hydrogen bonds, forming a three-dimensional framework.

Flow signatures and catchment's attributes for HCA clustering in a hydrologic similarity assessment (Tunisian case).

Partitioning methods such as cluster analysis are advantageous in pooling catchments into hydrometric similar regions. They help overcome data shortage in ungauged catchments, which is a common problem in Sud Mediterranean zones. Without accurate forecasts, it is difficult to assess and manage water resources efficiently this situation won't be of any assistance to hydrology decision-makers. This paper illustrates a Tunisian application case, that aims to pool catchments with a hierarchical clustering algorithm (HCA) based on distances calculated in multidimensional physiographical and hydrometric space. The homogeneity of generated clusters is checked by the silhouette index. Then the distances efficiencies are compared. Nineteen semi-arid Tunisian catchments monitored since 1992 are studied. Twelve physiographical attributes, nine rainfall and streamflow signatures are considered in the HCA with two clusters. Correlation distance provides the most homogeneous clusters. Statistically the: percentage of area affected by anti-erosive practices, percentage of forest cover and catchment area are the most discriminating attributes. However, hydrometrical signatures appear to be irrelevant. These partitions highlight two different hydrological behaviors that must support forecasting. Results are promising in the Sud-Mediterranean case, where the shortage of hydrometrical data is an ongoing problem. They have the advantage of enabling hydrologic forecasting without requiring heavy information.

Hydrogen bonding in 1-carb-oxy-propanaminium nitrate.

There are two crystallographically independent cations and two anions in the asymmetric unit of the title compound, C(4)H(5)NO(2) (+)·NO(3) (-). In the crystal, the 1-carb-oxy-propanaminium cations and nitrate anions are linked to each other through strong N-H⋯O and O-H⋯O hydrogen bonds, forming a three-dimensional complex network. C-H⋯O inter-actions also occur.

Soliton-self compression in highly nonlinear chalcogenide photonic nanowires with ultralow pulse energy.

We design As2Se3 and As2S3 chalcogenide photonic nanowires to optimize the soliton self-compression with short distances and ultralow input pulse energy. We numerically demonstrate the generation of single optical cycle in an As2S3 photonic nanowire: a 5.07 fs compressed pulse is obtained starting from 250 fs input pulse with 50 pJ in 0.84 mm-long As2S3 nanowire. Taking into account the high two photon absorption (TPA) coefficient in the As2Se3 glass, accurate modeling shows the compression of 250 fs down to 25.4 fs in 2.1 mm-long nanowire and with 10 pJ input pulse energy.

trans-Diaqua-bis-(dl-valinato-κN,O)nickel(II).

In the title complex, [Ni(C(5)H(9)NO(2))(2)(H(2)O)(2)], the Ni(II) atom, located on a centre of inversion, is trans-coordinated by two O atoms and two N atoms from d-bidentate valine and l-bidentate valine ligands and two water O atoms in an octa-hedral geometry. In the crystal, the discrete mononuclear units are linked into a three-dimensional network via O-H⋯O and N-H⋯O hydrogen bonds. C-H⋯O inter-actions are also observed.

Clinical and body composition predictors of bone turnover and mineral content in obese postmenopausal women.

The purpose of this study was to determine the predictors of bone mineral density (BMD), bone mineral content (BMC), and bone turnover markers in obese postmenopausal women. In this cross-sectional study, 81 postmenopausal women aged 58.40 ± 6.08 years were analyzed. Anthropometric parameters were recorded. Serum glucose parameters, serum lipid profiles, adipokines, renal, hepatic parameters, and bone markers concentrations were determined by well-validated laboratory routine methods. BMD, BMC, and body composition were measured by Dual X-ray Absorptiometry. We found a significant correlation of BMD with age, years since menopause, anthropometric parameters, glycemia, alkaline phosphatase, fat mass, and lean mass. Multiple regression analysis demonstrated that years since menopause, waist circumference, alkaline phosphatase, trunk fat, and lean mass were independently associated to BMD. Also, age, years since menopause, anthropometric parameters, total cholesterol, alkaline phosphatase, fat mass, and lean mass were correlated to BMC. However, only waist circumference and trunk fat were independently related to BMC. Bone turnover markers were significantly correlated to the age, glycemia, HbA1c, adipokines, hepatic parameters, and lean mass. Nevertheless, only adipokines, gamma glutamyl transferase (GGT), and alkaline phosphatase were independently associated to bone turnover markers. These observations suggest that number of years since menopause, waist circumference, alkaline phosphatase, trunk fat, and lean mass were the only significant predictors of BMD. However, waist circumference seems to be a stronger predictor than trunk fat for BMC. Moreover, adiponectin, resistin, GGT, and alkaline phosphatase were significant predictors of the bone resorption (CTX-I) and the bone formation (P1NP) markers.

Risk and Predictors of Postoperative Morbidity and Mortality After Pancreaticoduodenectomy for Pancreatic Neuroendocrine Neoplasms: A Comparative Study With Pancreatic Ductal Adenocarcinoma.

OBJECTIVES: Pancreaticoduodenectomy (PD) is associated with a high risk of postoperative complications and mortality. The aim of this study was to compare postoperative morbidity after PD in patients undergoing resections for pancreatic neuroendocrine neoplasms (PanNENs) with patients undergoing the same resection for pancreatic ductal adenocarcinoma (PDAC). METHODS: Data of 566 patients from 3 European tertiary referral centers between 1998 and 2014 were considered. RESULTS: Overall, 566 patients (179 with PanNENs, 387 with PDAC) who underwent PD were analyzed. Patients with PanNENs were significantly younger (56 vs 64 years, P < 0.0001). The consistency of the pancreas was soft in 147 patients (82%) with PanNENs and in 162 patients (42%) with PDAC (P < 0.0001). Patients in the PanNENs group had a significantly higher rate of pancreatic fistula (P < 0.0001), bile leak (P = 0.004), abdominal collection (P = 0.017), and development of sepsis (P = 0.042). No differences in terms of overall postoperative complications, median length of stay, and in-hospital mortality were found. On multivariate analysis sex (male), PanNENs indication, blood transfusion, and a soft pancreatic texture were independent predictors of pancreatic fistula after PD. CONCLUSIONS: Pancreaticoduodenectomy for PanNENs is associated with higher rate of surgical-specific postoperative complications than those for PDAC.

Nonlinear optical organic-inorganic crystals: synthesis, structural analysis and verification of harmonic generation in tri-(o-chloroanilinium nitrate).

The structural and nonlinear optical properties of a new anilinium hybrid crystal of chemical formula (C6H7NCl+·NO3-)3 have been investigated. The crystal structure was determined from single-crystal X-ray diffraction measurements performed at a temperature of 100 K which show that the compound crystallizes in a noncentrosymmetric space group (Pna21). The structural analysis was coupled with Hirshfeld surface analysis to evaluate the contribution of the different intermolecular interactions to the formation of supramolecular assemblies in the solid state that exhibit nonlinear optical features. This analysis reveals that the studied compound is characterized by a three-dimensional network of hydrogen bonds and the main contributions are provided by the O...H, C...H, H...H and Cl...H interactions, which alone represent ∼85% of the total contributions to the Hirshfeld surfaces. It is noteworthy that the halogen...H contributions are quite comparable with those of the H...H contacts. The nonlinear optical properties were investigated by nonlinear diffuse femtosecond-pulse reflectometry and the obtained results were compared with those of the reference material LiNbO3. The hybrid crystals exhibit notable second (SHG) and third (THG) harmonic generation which confirms its polarity is generated by the different intermolecular interactions. These measurements also highlight that the THG signal of the new anilinium compound normalized to its SHG counterpart is more pronounced than for LiNbO3.

The structural properties of a noncentrosymmetric polymorph of 4-aminobenzoic acid.

The crystal structure of a polymorph of 4-aminobenzoic acid (PABA), C7H7NO2, at 100 K is noncentrosymmetric, as opposed to centrosymmetric in the structures of the other known polymorphs. The two crystallographically independent PABA molecules form pseudocentrosymmetric O-H...O hydrogen-bonded dimers that are further linked by N-H...O hydrogen bonds into a three-dimensional network. The benzene rings stack in the b direction. The CO2 moieties are bent out slightly from the benzene ring plane.

A comparative study of two polymorphs of L-aspartic acid hydrochloride.

Two polymorphs of L-aspartic acid hydrochloride, C4H8NO4(+)·Cl(-), were obtained from the same aqueous solution. Their crystal structures have been determined from single-crystal data collected at 100 K. The crystal structures revealed three- and two-dimensional hydrogen-bonding networks for the triclinic and orthorhombic polymorphs, respectively. The cations and anions are connected to one another via N-H···Cl and O-H···Cl interactions and form alternating cation-anion layer-like structures. The two polymorphs share common structural features; however, the conformations of the L-aspartate cations and the crystal packings are different. Furthermore, the molecular packing of the orthorhombic polymorph contains more interesting interactions which seems to be a favourable factor for more efficient charge transfer within the crystal.

Sporadic nonfunctioning pancreatic neuroendocrine tumors: prognostic significance of incidental diagnosis.

BACKGROUND: Sporadic nonfunctioning pancreatic neuroendocrine tumors (NF-PNETs) are increasingly diagnosed as incidentalomas, and their resection is usually recommended. The prognostic significance of this diagnosis feature is poorly studied, and management of these tumors remains controversial. Clinical, pathologic characteristics and outcome of resected incidentally diagnosed NF-PNET (Inc) were compared with resected symptomatic NF-PNET (Symp) to better assess their biologic behavior and tailor their management. METHODS: From 1994 to 2010, 108 patients underwent resection for sporadic nonmetastatic NF-PNET. Diagnosis was considered as incidental in patients with no abdominal symptoms or symptoms unlikely to be related to tumor mass. Patients with Inc were compared with patients with Symp, regarding demographics, postoperative course, pathology, and disease-free survival (DFS). RESULTS: Of the 108 patients, 65 (61%) had incidentally diagnosed tumors. Pancreas-sparing pancreatectomies (enucleation/central pancreatectomy) were performed more frequently in Inc (62% vs 30%, P = .001). Inc tumors were more frequently <20 mm (65% vs 42%, P = .019), staged T1 (62% vs 33%, P = .0001), node negative (85% vs 60%; P = .005), and grade 1 (66% vs 33%, P = .0001). One postoperative death occurred in the Inc group, and postoperative morbidity was similar between the two groups (60% vs 65%, P = .59). DFS was substantially better in the Inc group (5-year DFS = 92% vs 82%, P = .0016). CONCLUSION: Incidentally diagnosed NF-PNETs are associated with less aggressive features compared with symptomatic lesions but cannot always be considered to be benign. Operative resection remains recommended for most. Incidentally diagnosed NF-PNET may be good candidates for pancreas-sparing pancreatectomies.

Pattern and clinical predictors of lymph node involvement in nonfunctioning pancreatic neuroendocrine tumors (NF-PanNETs).

IMPORTANCE: Nonfunctioning pancreatic neuroendocrine tumors (NF-PanNETs) are often indolent neoplasms without lymph node (LN) metastasis at diagnosis. Therefore, in patients with low risk of LN metastasis, the extent of surgery and lymphadenectomy could be limited and follow-up adjusted to the very low risk of relapse. OBJECTIVE: To construct a predicting model to assess the risk of pN+ prior to surgical resection for NF-PanNETs using preoperative retrievable variables. DESIGN: Retrospective review using multiple logistic regression analysis to construct predictive model of pN+ based on preoperatively available data. SETTING: The combined prospective databases of the Surgical Departments of the University of Verona, Verona, Italy, and Beaujon Hospital, Clichy, France, were queried for clinical and pathological data. PARTICIPANTS: All patients with resected (R0 or R1), pathologically confirmed NF-PanNETs between January 1, 1993 and December 31, 2009. MAIN OUTCOME AND MEASURE: Risk of lymph node metastases in patients with pancreatic neuroendocrine tumors. RESULTS: Among 181 patients, nodal metastases were reported in 55 patients (30%) and were associated with decreased 5-year disease-free survival (70% vs 97%, P < .001). Multivariable analysis showed that independent factors associated with nodal metastasis were radiological nodal status (rN) (odds ratio [OR], 5.58; P < .001) and tumor grade (NET-G2 vs NET-G1: OR, 4.87; P < .001) (first model). When the tumor grade was excluded, rN (OR, 4.73; P = .001) and radiological tumor size larger than 4 cm (OR, 2.67; P = .03) were independent predictors of nodal metastasis (second model). The area under the receiver operating characteristic curve for the first and second models were 80% and 74%, respectively. CONCLUSIONS AND RELEVANCE: Patients with NF-PanNET-G1 have a very low risk of pN+ in the absence of radiological signs of node involvement. When preoperative grading assessment is not achieved, the radiological size of the lesion is a powerful alternative predictor of pN+. The risk of pathological nodal involvement in patients with NF-PanNETs can be accurately estimated by a clinical predictive model.

Parenchyma-sparing resections for pancreatic neuroendocrine tumors.

BACKGROUND: Parenchyma-sparing pancreatectomy (PSP), including enucleation and central pancreatectomy, has been investigated as an alternative to standard resection for pancreatic endocrine neoplasm, but the benefit/risk of these procedures remains little known. METHODS: From 1998 to 2010, among 197 patients operated for well-differentiated pancreatic neuroendocrine tumors, 67 underwent PSP (45 enucleations and 22 central pancreatectomies) and 66 standard resections (35 pancreaticoduodenectomies and 31 distal pancreatectomies) for a tumor below 4 cm, without synchronous distant metastasis. Groups were compared regarding postoperative morbidity, mortality, long-term pancreatic function, and survival calculated using the Kaplan-Meier method. RESULTS: Tumors operated by PSP had a median size of 15 mm, were mainly incidentally diagnosed (n = 46, 69 %), and nonfunctioning (n = 55, 82 %). Overall morbidity rate was higher after PSP than standard resection (SR) (76 vs 58 %, p = 0.0028), including more frequent pancreatic fistulas (69 vs 42 %, p = 0.003). Postoperative diabetes was less frequent following PSP than pancreaticoduodenectomy (5 vs 21 %; p = 0.022) but equivalent to the one observed after distal pancreatectomy (4 %, p = 1). Exocrine insufficiency was significantly less frequent after PSP than SR (3 vs 32 %; p < 0.0001). The overall and recurrence-free 5-year survival after PSP for nonfunctioning tumors was 96 and 98 %, respectively. CONCLUSION: In selected patients, with small and low-grade tumors, PSP are associated with excellent overall and recurrence-free survivals. These procedures are associated with an increased postoperative morbidity but an excellent postoperative pancreatic function. Therefore, they should be considered as a valid therapeutic option in selected well-differentiated pancreatic neuroendocrine tumors.