Liquid crystal wave plate operating close to 18†THz.

Controlling the properties of mid- and far-infrared radiation can provide a means to transiently alter the properties of materials for novel applications. However, a limited number of optical elements are available to control its polarization state. Here we show that a 15-µm thick liquid crystal cell containing 8CB (4-octyl-4'-cyanobiphenyl) in the ordered, smectic A phase can be used as a phase retarder or wave plate. This was tested using the bright, short-pulsed (∼1 ps) radiation centered at 16.5 µm (18.15 THz) that is emitted by a free electron laser at high repetition rate (13 MHz). These results demonstrate a possible tool for the exploration of the mid- and far-infrared range and could be used to develop novel metamaterials or extend multidimensional spectroscopy to this portion of the electromagnetic spectrum.

Prognostic Factors across Poorly Differentiated Neuroendocrine Neoplasms: A Pooled Analysis.

INTRODUCTION: Poorly differentiated neuroendocrine carcinomas (NECs) are characterized by aggressive clinical course and poor prognosis. No reliable prognostic markers have been validated to date; thus, the definition of a specific NEC prognostic algorithm represents a clinical need. This study aimed to analyze a large NEC case series to validate the specific prognostic factors identified in previous studies on gastro-entero-pancreatic and lung NECs and to assess if further prognostic parameters can be isolated. METHODS: A pooled analysis of four NEC retrospective studies was performed to evaluate the prognostic role of Ki-67 cut-off, the overall survival (OS) according to primary cancer site, and further prognostic parameters using multivariable Cox proportional hazards model and machine learning random survival forest (RSF). RESULTS: 422 NECs were analyzed. The most represented tumor site was the colorectum (n = 156, 37%), followed by the lungs (n = 111, 26%), gastroesophageal site (n = 83, 20%; 66 gastric, 79%) and pancreas (n = 42, 10%). The Ki-67 index was the most relevant predictor, followed by morphology (pure or mixed/combined NECs), stage, and site. The predicted RSF response for survival at 1, 2, or 3 years showed decreasing survival with increasing Ki-67, pure NEC morphology, stage III-IV, and colorectal NEC disease. Patients with Ki-67 <55% and mixed/combined morphology had better survival than those with pure morphology. Morphology pure or mixed/combined became irrelevant in NEC survival when Ki-67 was ≥55%. The prognosis of metastatic patients who did not receive any treatment tended to be worse compared to that of the treated group. The prognostic impact of Rb1 immunolabeling appears to be limited when multiple risk factors are simultaneously assessed. CONCLUSION: The most effective parameters to predict OS for NEC patients could be Ki-67, pure or mixed/combined morphology, stage, and site.

Isolating Attosecond Electron Dynamics in Molecules where Nuclei Move Fast.

Capturing electronic dynamics in real time has been the ultimate goal of attosecond science since its beginning. While for atomic targets the existing measurement techniques have been thoroughly validated, in molecules there are open questions due to the inevitable copresence of moving nuclei, which are not always mere spectators of the phototriggered electron dynamics. Previous work has shown that not only can nuclear motion affect the way electrons move in a molecule, but it can also lead to contradictory interpretations depending on the chosen experimental approach. In this Letter we investigate how nuclear motion affects and eventually distorts the electronic dynamics measured by using two of the most popular attosecond techniques, reconstruction of attosecond beating by interference of two-photon transitions and attosecond streaking. Both methods are employed, in combination with ab initio theoretical calculations, to retrieve photoionization delays in the dissociative ionization of H_{2}, H_{2}→H^{+}+H+e^{-}, in the region of the Q_{1} series of autoionizing states, where nuclear motion plays a prominent role. We find that the experimental reconstruction of attosecond beating by interference of two-photon transitions results are very sensitive to bond softening around the Q_{1} threshold (27.8 eV), even at relatively low infrared (IR) intensity (I_{0}∼1.4×10^{11} W/cm^{2}), due to the long duration of the probe pulse that is inherent to this technique. Streaking, on the other hand, seems to be a better choice to isolate attosecond electron dynamics, since shorter pulses can be used, thus reducing the role of bond softening. This conclusion is supported by very good agreement between our streaking measurements and the results of accurate theoretical calculations. Additionally, the streaking technique offers the necessary energy resolution to accurately retrieve the fast-oscillating phase of the photoionization matrix elements, an essential requirement for extending this technique to even more complicated molecular targets.

Does ProCore Fine-Needle Biopsy Really Improve the Clinical Outcome of Endoscopic Ultrasound-Guided Sampling of Pancreatic Masses?

INTRODUCTION: Fine-needle biopsy (FNB) has been suggested to provide better histological samples as compared to endoscopic ultrasound fine-needle aspiration (EUS-FNA). However, studies comparing EUS-FNA and EUS-FNB for pancreatic lesions reported contrasting results. The aim of this study was to compare the clinical performance of EUS-FNA versus EUS-FNB with the ProCore needle for the investigation of pancreatic lesions. METHODS: We reviewed all patients undergoing EUS for the investigation of pancreatic lesions from August 2012 to September 2018. From August 2012 to January 2015, all procedures were performed with standard needles, whereas from February 2015 to September 2018, the use of ProCore needles had been introduced. Data on diagnostic accuracy, number of needle passes, and/or adverse events were collected. RESULTS: Three hundred twenty-four patients were retrospectively evaluated: 190 (58.6%) underwent EUS-FNA and 134 (41.4%) EUS-FNB. Both EUS-FNA and EUS-FNB showed high diagnostic accuracy for malignancy (94% [95% CI: 89-97%] vs. 94% [95% CI: 89-98%]). Notably, there were no differences between EUS-FNA and EUS-FNB in terms of sensitivity, specificity, positive and negative likelihood ratio, histological core tissue retrieval, adverse events, or number of needle passes. However, subgroup analysis noted a higher diagnostic accuracy for 25G EUS-FNB as compared to 25G EUS-FNA (85.7 vs. 55.5%; *p = 0.023). CONCLUSION: EUS-FNB with the ProCore needle is safe and feasible in pancreatic lesions. The ProCore needle did not provide any advantage in terms of diagnostic accuracy, sensitivity, specificity, positive and/or negative likelihood ratio, or acquisition of the core specimen; therefore, its routine application is not supported.

Prognostic Impact of Primary Side and RAS/RAF Mutations in a Surgical Series of Colorectal Cancer with Peritoneal Metastases.

BACKGROUND: Selecting patients with colorectal cancer peritoneal metastases (CRC-PMs) for surgery is still a concern. Biological features have the potential to improve prognostic stratification, but their significance in this clinical setting is still unclear. We assessed the prognostic impact of primary side and KRAS/NRAS/BRAF/PIK3CA mutations in patients treated with either cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) or CRS alone. METHODS: We reviewed a prospective database of 152 CRC-PM patients selected to undergo perioperative systemic chemotherapy and CRS with or without HIPEC. Extensive mutational analysis of KRAS, NRAS, BRAF, and PIK3CA was performed by polymerase chain reaction (PCR). In 68 patients, Ion Torrent next-generation sequencing technology was used to characterize the hotspot regions of 50 genes. RESULTS: The primary tumor was right-sided in 61 patients (40.1%) and left-sided in 91 patients (59.9%). Right-sided primaries were associated with mutated KRAS (p = 0.01) and normal carcinoembryonic antigen (CEA; p = 0.03). KRAS was mutated in 71/152 patients (46.7%), NRAS in 7/152 patients (4.6%), BRAF in 10/152 patients (6.6%), PIK3CA in 17/78 patients (25.0%), TP53 in 37/68 patients (54.4%), APC in 25/68 patients (36.7%), SMAD4 in 13/68 patients (19.1%), and FBXW7 in 5/68 patients (7.4%). Median follow-up was 54.9 months and median survival from PM diagnosis was 45.1 months. The right-sided primary (hazard ratio [HR] 1.62, 95% confidence interval [CI] 0.43-0.89; p = 0.011), BRAF mutations (HR 2.21, 95% CI 1.05-4.63; p = 0.038), and Peritoneal Cancer Index (HR 1.47, 95% CI 1.03-2.10; p = 0.036) independently correlated with poorer survival, while APC mutations univariately correlated with better survival (p = 0.03). CONCLUSIONS: BRAF mutations and right-sided primary are adverse prognostic factors that may be used to optimize therapeutic strategies. APC may be involved in CRC-PM development and progression.

Ki-67 Index of 55% Distinguishes Two Groups of Bronchopulmonary Pure and Composite Large Cell Neuroendocrine Carcinomas with Distinct Prognosis.

BACKGROUND: Little information is available concerning prognostic factors for bronchopulmonary large cell neuroendocrine carcinomas (BP-LCNECs) and even less is known about combined LCNECs (Co-LCNECs). We investigated whether an integrated morphological, immunohistochemical, and molecular approach could be used for their prognostic evaluation. METHODS: Morphological (including combined features), proliferative (mitotic count/Ki-67 index), immunohistochemical (napsin A, p40, TTF-1, CD44, OTP, SSTR2A, SSTR5, mASH1, p53, RB1, and MDM2), and genomic (TP53, RB1, ATM, JAK2, KRAS, and STK11) findings were analyzed in BP-LCNECs from 5 Italian centers, and correlated with overall survival (OS). The Ki-67 index was expressed as the percentage of positive cells in hot spots as indicated in the WHO 2019 Digestive System Tumors and, for Co-LCNECs, the Ki-67 index was evaluated only in the LCNEC component. RESULTS: A total of 111 LCNECs were distinguished into 70 pure LCNECs, 35 Co-LCNECs (27 with adenocarcinoma [ADC] and 8 with squamous cell carcinoma [SqCC]), and 6 LCNECs with only napsin A immunoreactivity. The Ki-67 index cutoff at 55% evaluated in the neuroendocrine component was the most powerful predictor of OS (log-rank p = 0.0001) in all LCNECs; 34 cases had a Ki-67 index <55% (LCNEC-A) and 77 had a Ki-67 index ≥55% (LCNEC-B). Statistically significant differences in OS (log-rank p = 0.0001) were also observed between pure and Co-LCNECs. A significant difference in OS was found between pure LCNECs-A and Co-LCNECs-A (p < 0.05) but not between pure LCNECs-B and Co-LCNECs-B. Co-LCNEC-ADC and LCNEC napsin A+ cases had longer OS than pure LCNEC and Co-LCNEC-SqCC cases (log-rank p = 0.0001). On multivariable analysis, tumor location, pure versus combined features, and napsin A, but no single gene mutation, were significantly associated with OS after adjustment for Ki-67 index and study center (p < 0.05). CONCLUSIONS: The Ki-67 proliferation index and the morphological characterization of combined features in LCNECs seem to be important tools for predicting clinical outcome in BP-LCNECs.

Medulloblastoma and familial adenomatous polyposis: Good prognosis and good quality of life in the long-term?

INTRODUCTION: Mutations of the APC (adenomatous polyposis coli) gene correlate mainly with familial adenomatous polyposis (FAP), but can occasionally be pathogenic for medulloblastoma (MBL) wingless-related integration site (WNT) subtype, the course of which has only recently been described. METHODS: We retrieved all patients with documented germline APC mutations and a diagnosis of MBL to examine their outcome, late effects of treatment, and further oncological events. RESULTS: Between 2007 and 2016, we treated six patients, all with a pathogenic APC variant mutation and all with MBL, classic histotype. None had metastatic disease. All patients were in complete remission a median 65 months after treatment with craniospinal irradiation at 23.4 Gy, plus a boost on the posterior fossa/tumor bed up to 54 Gy, followed by cisplatin/carboplatin, lomustine, and vincristine for a maximum of eight courses. Five of six diagnostic revised MRI were suggestive of the WNT molecular subgroup typical aspects. Methylation profile score (in two cases) and copy number variation analysis (chromosome 6 deletion in two cases) performed on four of six retrieved samples confirmed WNT molecular subgroup. Four out of six patients had a positive family history of FAP, while gastrointestinal symptoms prompted its identification in the other two cases. Four patients developed other tumors (desmoid, MELTUMP, melanoma, pancreatoblastoma, thyroid Tir3) from 5 to 7 years after MBL. DISCUSSION: Our data confirm a good prognosis for patients with MBL associated with FAP. Patients' secondary tumors may or may not be related to their syndrome or treatment, but warrant adequate attention when planning shared guidelines for these patients.

Clinical Behavior and Treatment Response of Epstein-Barr Virus-Positive Metastatic Gastric Cancer: Implications for the Development of Future Trials.

BACKGROUND: Epstein-Barr virus (EBV)-positive gastric cancers (GCs) have been recently identified as a molecular subgroup showing excellent outcomes after surgery for early-stage disease and responsiveness to immune checkpoint inhibitors (ICIs) for metastatic stage. No data are available on the prevalence, clinical characteristics, and prognosis of this subgroup of GCs in the metastatic setting. MATERIALS AND METHODS: In this cohort study, we assessed the impact of EBV status in patients with metastatic GC treated with chemotherapy at two Italian institutions. RESULTS: Among the 175 cases analyzed, only 7 (4%) were EBV positive and all showed long-lasting and even complete responses to first-line chemotherapy with fluorouracil and platinum and a significantly better survival compared with EBV-negative patients (3-year overall survival: 80% vs. 20.1%; hazard ratio: 0.12). CONCLUSION: If confirmed in larger data sets, our results may give a strong rationale for investigating the addition of ICIs to chemotherapy, in order to maximize the chance of achieving durable and complete responses in this uncommon subtype of GC. IMPLICATIONS FOR PRACTICE: To date, no data are available on the prevalence and clinical characteristics of patients with Epstein-Barr virus (EBV)-positive metastatic gastric cancer (GC), a specific subtype of GC showing excellent outcomes after radical surgery in early-stage disease and responsiveness to immune checkpoint inhibitors (ICIs). This cohort study showed that patients with EBV-positive GC who did not receive ICIs had exceptional, long-lasting, and even complete responses to first-line chemotherapy with fluorouracil and platinum and a significantly better survival compared with EBV-negative patients. If confirmed in larger series, these results may give a strong rationale for investigating the combination of chemotherapy and ICIs to achieve durable and potentially complete response in this uncommon subtype of GC.

Attosecond resolution from free running interferometric measurements.

Attosecond measurements reveal new physical insights in photoionization dynamics from atoms, molecules and condensed matter. However, on such time scales even a small timing jitter can significantly reduce the time resolution in pump-probe measurements. Here, we propose a novel technique to retrieve attosecond delays from a well-established attosecond interferometric technique, referred to as reconstruction of attosecond beating by interference of two-photon transition (RABBITT), which is unaffected by timing jitter and significantly improves the precision of state-of-the-art experiments. We refer to this new technique as the timing-jitter unaffected rabbitt time delay extraction method, in short TURTLE. Using this TURTLE technique we could measure the attosecond ionization time delay between argon and neon in full agreement with prior measurements. The TURTLE technique allows for attosecond time resolution without pump-probe time delay stabilization and without attosecond pulses because only a stable XUV frequency comb is required as a pump. This will more easily enable attosecond measurements at FELs, for example, and thus provide a valuable tool for attosecond science. Here we also make a MATLAB code available for the TURTLE fit with appropriate citation in return.

A proposal of an updated classification for pelvic relapses of rectal cancer to guide surgical decision-making.

BACKGROUND AND OBJECTIVES: Selection of patients affected by pelvic recurrence of rectal cancer (PRRC) who are likely to achieve a R0 resection is mandatory. The aim of this study was to propose a classification for PRRC to predict both radical surgery and disease-free survival (DFS). METHODS: PRRC patients treated at the National Cancer Institute of Milan (Italy) were included in the study. PRRC were classified as S1, if located centrally (S1a-S1b) or anteriorly (S1c) within the pelvis; S2, in case of sacral involvement below (S2a) or above (S2b) the second sacral vertebra; S3, in case of lateral pelvic involvement. RESULTS: Of 280 reviewed PRRC patients, 152 (54.3%) were evaluated for curative surgery. The strongest predictor of R+ resection was the S3 category (OR, 6.37; P = .011). Abdominosacral resection (P = .012), anterior exenteration (P = .012) and extended rectal re-excision (P = .003) were predictive of R0 resection. S3 category was highly predictive of poor DFS (HR 2.53; P = .038). DFS was significantly improved after R0 surgery for S1 (P < .0001) and S2 (P = .015) patients but not for S3 cases (P = .525). CONCLUSIONS: The proposed classification allows selection of subjects candidates to curative surgery, emphasizing that lateral pelvic involvement is the main predictor of R+ resection and independently affects the DFS.

Results of a multicenter universal newborn screening program for sickle cell disease in Italy: A call to action.

BACKGROUND: Sickle cell disease (SCD) is a chronic multisystem disorder requiring comprehensive care that includes newborn screening (NBS) as the first step of care. Italy still lacks a national SCD NBS program and policy on blood disorders. Pilot single-center screening programs and a regional targeted screening have been implemented so far, but more evidence is needed in order to impact health policies. POPULATION AND METHODS: NBS was offered to parents of newborns in gynecology clinics in Padova and Monza, tertiary care university hospitals in northern Italy. High-performance liquid chromatography (HPLC) was performed as the first test on samples collected on Guthrie cards. Molecular analysis of the beta-globin gene was performed on positive samples. RESULTS: A total of 5466 newborns were enrolled; for 5439, informed consents were obtained. A similar family origin was seen in the two centers (65% Italians, 9% mixed couples, 26% immigrants). Compared with SCD NBS programs in the United States and Europe, our results show a similar incidence of SCD patients and carriers. All SCD patients had a Sub-Saharan family background; HbS carriers were 15% Caucasians (Italian, Albanians) and 10% from other areas (North Africa-India-South America); carriers of other hemoglobin variants were mainly (47%) from other areas. CONCLUSIONS: Our results demonstrate the feasibility of a multicentric NBS program for SCD, give information on HbS epidemiology in two Northern Italian Areas, and support previous European recommendation for a universal NBS program for SCD in Italy: a high incidence of patients and carriers has been detected, with a high percentage of Caucasian carriers, impossible to identify in a targeted NBS.

Prognostic impact of regression in patients with primary cutaneous melanoma >1 mm in thickness.

BACKGROUND: The impact of histologic regression on sentinel lymph node biopsy (SLNB) status and on clinical outcome is uncertain. OBJECTIVE: To investigate whether and to what extent regression <75% is able to predict SLNB status and clinical outcome of patients with melanoma >1-mm thick. METHODS: The study included patients with diagnoses given at 4 centers of the Italian Melanoma Intergroup. Univariate and multivariate Cox proportional hazard models stratified by center were used to analyze the effect of regression on disease-free interval and melanoma-specific survival. RESULTS: Out of 1182 patients given primary cutaneous melanoma diagnoses during 1998-2015 with a Breslow thickness >1 mm, 954 (304 with and 650 without regression) were included in the analysis. The proportion of patients with a positive SLNB was lower in patients with regression than without (24.4% vs 31.6%, chi-squared test P = .0368). At multivariate analysis, no association was detected between regression and disease-free interval (hazard ratio 1.11, 95% confidence interval 0.85-1.46; P = .4509) or melanoma-specific survival (hazard ratio 1.05, 95% confidence interval 0.77-1.44; P = .7600). LIMITATION: Retrospective analysis. CONCLUSION: In our series, regression was not an independent prognostic factor in primary cutaneous melanoma patients with Breslow thickness >1 mm whereas it was associated with a lower incidence of SLNB positivity.

Serenoa repens extracts: In vitro study of the 5α-reductase activity in a co-culture model for Benign Prostatic Hyperplasia.

OBJECTIVES: Benign Prostatic Hyperplasia (BPH) is a form of benign tumor that occurs in humans mainly with ageing. It affects more than 50% of over 50 years old males and it is characterized by an increased synthesis of dihydrotestosterone (DHT), due to the 5α-reductase activity. The BPH therapeutic approach mainly uses 5α-reductase inhibitors, such as the active compounds present in the extracts deriving from species Serenoa repens. Many lipidosterolic extracts are available on the market, which are obtained with different solvents, among them ethanol is recognized as non-toxic and has less handling risks than hexane. The purpose of the present experimental study was to investigate in-vitro the potency of an ethanol extract of S. repens comparing it with an n-hexane one. MATERIALS AND METHODS: Two different lipido-sterolic extracts of S. repens have been tested: ethanol extract and n-hexane extract, two batches for each one. The inhibitory action of the extract was evaluated estimating in-vitro the activity of enzyme 5α-reductase type I (5α-RI), which was mainly active under the experimental condition of pH 7.5. DHT amount, synthesized from testosterone (1 µM), was evaluated in a co-culture model of epithelial cells and fibroblasts resulting from prostatic biopsy of a patient with BPH. RESULTS: The analysis of the resulting dose-response curves showed that the entire S. repens extracts inhibited the 5α-RI showing no difference between the two kinds of extract or between the batches. The resulting IC50 values were the following: 8.809 (95% CI = 5.133-15.56) and 9.464 (95% CI = 5.094- 18.27) for ethanol extracts; 11.08 (95% CI = 6.389-19.98) and 12.72 (95% CI = 7.758-21.53) for n-hexane extracts. CONCLUSIONS: The potency of ethanol extracts of S. repens was comparable with the one of n-hexane extracts.

Mitotic rate correlates with sentinel lymph node status and outcome in cutaneous melanoma greater than 1 millimeter in thickness: A multi-institutional study of 1524 cases.

BACKGROUND: The 7th edition of the TNM American Joint Committee on Cancer classification incorporates mitotic rate (MR) only for primary cutaneous melanoma (PCM) with Breslow thickness (BT) ≤1 mm. OBJECTIVE: To investigate whether and to what extent MR is able to predict sentinel lymph node (SLN) status and clinical outcome of PCM patients with BT >1 mm. METHODS: The study included consecutive patients with PCM. Logistic regression and Cox regression model were used to analyze the impact of MR on SLN status, disease-free survival (DFS), and overall survival. RESULTS: From 1998 to 2015, 1524 PCM (median age 57.8 years) cases were diagnosed with a BT >1 mm in six centers of the Italian Melanoma Intergroup. Median follow-up was 5.0 years. By multivariate analysis, MR was associated with SLN positivity (odds ratio 1.98, 95% confidence interval [CI] 1.12-3.50, P = .018). After adjusting for BT, ulceration, age, sex, and SLN status, MR correlated with a poor DFS (hazard ratio 1.52, 95% CI 1.18-1.97, P = .002) and overall survival (hazard ratio 1.63, 95% CI 1.17-2.29, P = .004). LIMITATIONS: Retrospective analysis. CONCLUSION: MR is an independent prognostic factor for PCM patients with BT >1 mm. Incorporating this tissue biomarker could provide a better stratification of patients entering clinical trials in the adjuvant setting.

Electric field generation of Skyrmion-like structures in a nematic liquid crystal.

Skyrmions are particle-like topological objects that are increasingly drawing attention in condensed matter physics, where they are connected to inversion symmetry breaking and chirality. Here we report the generation of stable Skyrmion-like structures in a thin nematic liquid crystal film on chemically patterned patchy surfaces. Using the interplay of material elasticity and surface boundary conditions, we use a strong electric field to quench the nematic liquid crystal from a fully aligned phase to vortex-like nematic liquid crystal structures, centered on patterned patches, which carry two different sorts of topological defects. Numerical calculations reveal that these are Skyrmion-like structures, seeded from the surface boojum topological defects and swirling towards the second confining surface. These observations, supported by numerical methods, demonstrate the possibility to generate, manipulate and study Skyrmion-like objects in nematic liquid crystals on patterned surfaces.

Ultrafast all-optical response of a nematic liquid crystal.

Liquid crystals are superior optical materials for large area displays, but it is considered that their collective and slow-millisecond response makes them useless for ultrafast optical applications. In contrast to that, we here demonstrate an ultrafast optical response of a nematic liquid crystal, which is induced by an intense femtosecond optical impulse. We show that the refractive index of the nematic liquid crystal pentyl-cyanobiphenyl can be modulated at a time scale as fast as 500 fs via a coherently excited optical Kerr effect. The change in the refractive index is in the order of 10-4 at a fluence of 4 mJ/cm2 and is strongly polarization dependent. This unprecedented result opens new ways towards ultrafast all-optical modulation in liquid crystal-based devices.

Gaining control through frustration: two-fold approach for Liquid Crystal three-dimensional command layers.

The alignment of Liquid Crystal (LC) molecules, essential for their applications in optical devices such as displays, is usually controlled by functionalizing their confining surfaces by either patterning or by specific surfactants that induce either parallel or perpendicular molecular arrangement. Inducing a bistable alignment, such as in the new zenithal bistable displays, offers new opportunities in terms of new functionalities and lower energy consumption but a full understanding of such bistable alignment appears still complicated. Here we present a simple phenomenological model that includes surface topography and chemistry. The predicted orientational transitions and bistable states are in excellent agreement with experiments, thus making this a proper tool to design multistable 3D command layers.

Unveiling Low THz Dynamics of Liquid Crystals: Identification of Intermolecular Interaction among Intramolecular Modes.

Liquid crystals have found a wide area of application over the last few decades, proving to be excellent materials for tunable optics from visible to near-infrared frequencies. Currently, much effort is devoted to demonstrating their applicability at THz frequencies (1-10 THz), where tremendous advances of broadband and intense sources have been achieved. Yet, a detailed understanding of THz-triggered dynamics in liquid crystals is incomplete. Here, we perform broadband THz time domain spectroscopy on 4-cyano-4'-alkyl-biphenyl (nCB) and 5-phenylcyclohexanes (PCH5) across mesophases. Density functional theory calculations on isolated molecules capture the majority of the response. In particular, the pronounced modes around 4.5 and 5.5 THz mainly originate from bending modes of the cyano group. In contrast, the broad response below 3 THz, linked to modes of the alkyl chain, disagrees with the single molecule calculation. Here, we identify a clear intermolecular character of the response, supported by dimer and trimer calculations.

Liquid crystal-based temperature-controlled recirculating flat jet system.

In this paper, the design and implementation of a temperature-controlled recirculating flat jet system for liquid crystals (LCs)-based experiments are presented. In these experiments, the target liquid is usually exposed to medium to high laser fluences, possibly resonant with specific excitation, thus resulting in a change of local temperature and sudden degradation. To overcome this problem, each laser pulse must interact with a new volume of liquid, preferably with flat surfaces, while avoiding the use of substrates. A well-established solution consists of impinging two identical laminar jets that force the liquid into a radial expansion perpendicular to the plane formed by the jets, resulting in a consecutive chain of flat sheets bound by thick rims. In this context, LCs pose several challenges considering their viscosity, non-Newtonian behavior, and mesophase nature. Here, a precise control of temperature, thus mesophase, and pressure is demonstrated enabling the use of LCs in an impinging jet system. In particular, the system presented here delivers stable fluid chains of different sizes and thicknesses. The viscosity and non-Newtonian behavior of the LCs have a significant impact on the thickness of the chains as a function of the nozzle inner diameter, impinging angle, and radial distance from the impinging point. The flow rate, on the other hand, primarily affects the width and length of the liquid sheet.