Please identify all the named entities mentioned in the input sentence provided below. Use only the categories: PER - person, ORG - organization, and LOC - location.
Remember, nationalities are neither locations nor organizations, and organizations can represent other groups of people.
Pay attention to the provided example. You should only output the results in JSON format, following a similar structure to the example result provided.

Example sentence and results:

“While much of the digital transition is unprecedented in the United States, the peaceful transition of power is not,” Obama special assistant Kori Schulman wrote in a blog post Monday.

"Results": [
    {
        "TypeName": "LOC",
        "Text": "United States",
        "Start": 62,
        "End": 75
    },
    {
        "TypeName": "ORG",
        "Text": "Obama",
        "Start": 119,
        "End": 124
    },
    {
        "TypeName": "PER",
        "Text": "Kori Schulman",
        "Start": 143,
        "End": 156
    }
]

Considering the input sentence below, what is the output result?

Researchers have been investigating potential for male hormonal contraceptives for around 20 years.


"Results": []