89 research outputs found
Universal charts for optical difference frequency generation in the terahertz domain
We present a universal and rigorous approach to study difference frequency
generation in the terahertz domain, keeping the number of degrees of freedom to
a minimum, through the definition of a suitable figure of merit. The proposed
method relies on suitably normalized charts, that enable to predict the
optical-to-terahertz conversion efficiency of any system based on wave
propagation in quadratic nonlinear materials. The predictions of our approach
are found to be in good agreement with the best experimental results reported
to date, enabling also to estimate the d22 nonlinear coefficient of high
quality GaSe.Comment: 3 pages in 2 columns format, 3 figures. GaSe analysis has been
corrected. Fig. 3 has been replace
The role of nonlinear optical absorption in narrow-band difference frequency terahertz-wave generation
We present a general analysis of the influence of nonlinear optical
absorption on terahertz generation via optical difference frequency generation,
when reaching for the quantum conversion efficiency limit. By casting the
equations governing the process in a suitably normalized form, including either
two-photon- or three-photon-absorption terms, we have been able to plot
universal charts for phase matched optical-to-terahertz conversion for
different values of the nonlinear absorption coefficients. We apply our
analysis to some experiments reported to date, in order to understand to what
extent multiphoton absorption could have played a role and also to predict the
maximum achievable conversion efficiency at higher peak pump intensities.Comment: 16 pages, 2 figures. Some correction and some explanation adde
Exploiting the optical quadratic nonlinearity of zincblende semiconductors for guided-wave terahertz generation: a material comparison
We present a detailed analysis and comparison of dielectric waveguides made
of CdTe, GaP, GaAs and InP for modal phase matched optical difference frequency
generation (DFG) in the terahertz domain. From the form of the DFG equations,
we derived the definition of a very general figure of merit (FOM). In turn,
this FOM enabled us to compare different configurations, by taking into account
linear and nonlinear susceptibility dispersion, terahertz absorption, and a
rigorous evaluation of the waveguide modes properties. The most efficient
waveguides found with this procedure are predicted to approach the quantum
efficiency limit with input optical power in the order of kWs.Comment: 8 pages in two columns format, 6 figures, 2 Table
Glycosaminoglycan diversity in marine sponge extracellular matrix
Aim of this paper is to report on a screening on sponge ECM glycosaminoglycan (GAG) diversity.
To investigate the heterogeneity of sponge extracellular sulphated glycans, we determined their
content and distribution in some Mediterranean and Caribbean species. To focus on biological and
morpho-functional roles of these molecules in the sponge ECM some selected species were
considered as models to investigate the topographic distribution of GAGs in sponge body
according with the different architecture of specialized regions
Colorectal Cancer Stage at Diagnosis Before vs During the COVID-19 Pandemic in Italy
IMPORTANCE Delays in screening programs and the reluctance of patients to seek medical
attention because of the outbreak of SARS-CoV-2 could be associated with the risk of more advanced
colorectal cancers at diagnosis.
OBJECTIVE To evaluate whether the SARS-CoV-2 pandemic was associated with more advanced
oncologic stage and change in clinical presentation for patients with colorectal cancer.
DESIGN, SETTING, AND PARTICIPANTS This retrospective, multicenter cohort study included all
17 938 adult patients who underwent surgery for colorectal cancer from March 1, 2020, to December
31, 2021 (pandemic period), and from January 1, 2018, to February 29, 2020 (prepandemic period),
in 81 participating centers in Italy, including tertiary centers and community hospitals. Follow-up was
30 days from surgery.
EXPOSURES Any type of surgical procedure for colorectal cancer, including explorative surgery,
palliative procedures, and atypical or segmental resections.
MAIN OUTCOMES AND MEASURES The primary outcome was advanced stage of colorectal cancer
at diagnosis. Secondary outcomes were distant metastasis, T4 stage, aggressive biology (defined as
cancer with at least 1 of the following characteristics: signet ring cells, mucinous tumor, budding,
lymphovascular invasion, perineural invasion, and lymphangitis), stenotic lesion, emergency surgery,
and palliative surgery. The independent association between the pandemic period and the outcomes
was assessed using multivariate random-effects logistic regression, with hospital as the cluster
variable.
RESULTS A total of 17 938 patients (10 007 men [55.8%]; mean [SD] age, 70.6 [12.2] years)
underwent surgery for colorectal cancer: 7796 (43.5%) during the pandemic period and 10 142
(56.5%) during the prepandemic period. Logistic regression indicated that the pandemic period was
significantly associated with an increased rate of advanced-stage colorectal cancer (odds ratio [OR],
1.07; 95%CI, 1.01-1.13; P = .03), aggressive biology (OR, 1.32; 95%CI, 1.15-1.53; P < .001), and stenotic
lesions (OR, 1.15; 95%CI, 1.01-1.31; P = .03).
CONCLUSIONS AND RELEVANCE This cohort study suggests a significant association between the
SARS-CoV-2 pandemic and the risk of a more advanced oncologic stage at diagnosis among patients
undergoing surgery for colorectal cancer and might indicate a potential reduction of survival for
these patients
- …